DE29724717U1 - High density connector assembly - Google Patents

Description

High Density Connector Assembly Background of the Invention: Field of the Invention:

The present invention relates to electrical connectors and, more particularly, to high input/output density connector assemblies, such as array connectors.

Brief description of the state of the art:

The trend to reduce the size of electronic devices, particularly the size of portable devices, and to provide such devices with additional functions has led to a continued miniaturization of all components, particularly electrical connectors. Efforts to miniaturize connectors have included reducing the spacing between contacts in single-row or double-row linear connectors so that a relatively high number of input/output or other conductors can be interconnected by connectors that fit on narrowly defined areas of printed circuit boards designed to accommodate connectors. The trend toward miniaturization has also been accompanied by a shift toward favoring surface mount technology (SMT) for attaching components to printed circuit boards. The confluence of increased

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components on printed circuit boards. The combination of the increased use of surface mounting and the required fine pitch of linear connectors has led to the limits of surface mount technology being approached for high volume and low cost manufacturing. Reducing the spacing between contacts increases the risk of shorting adjacent solder joints or contacts during solder paste reflow. To meet the demand for increased input/output density, array connectors have been proposed. Such connectors comprise a two-dimensional matrix of contacts mounted on an insulating substrate and can achieve improved density. However, these connectors present certain difficulties in their attachment to printed circuit boards by surface mount technology, since the tips of most, if not all, contacts must be close to the connector body. It follows that the assembly techniques used must be very reliable, since it is difficult to visually inspect the solder joints or to repair them if they are faulty. In mounting an integrated circuit (IC) on a plastic or ceramic substrate, the use of a ball grid array (BGA) and other similar packaging patterns has become common. In a BGA array, solder balls attached to the integrated circuit assembly are positioned on the electrical contact pads of a circuit substrate on which a layer of solder paste has been deposited, usually using a shield or mask. The whole is then heated to a temperature at which the solder paste and at least some or all of the solder ball melt and bond to an underlying conductive pad formed on the circuit substrate.

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The integrated circuit is thus connected to the substrate without the need to connect external wires to the IC.

Many recent patents are directed to measures for miniaturizing products that use surface mount technology.

For example, WO 98/15990 describes a ball grid array (BGA) technology applied to a flat board-to-board connection system, where only a reduction in the overall height is required. For this purpose, the contacts and soldering elements are designed to be as compact as possible.

WO 97/20454 describes a high-density connector capable of connecting an electronic assembly comprising a solder element and a circuit board, in which the contact has a surface mounting region with a convex bottom surface whose shape forms at least the lower region of a sphere and thus depicts a solder ball.

US-A-5 593 322 relates to a high density connector with fusible ball contacts located on the bottom surface of a connector for connecting a component to the surface of a printed circuit board in well-known BGA technology in which plastic carriers provided with metal strips on their four surfaces are connected to a contact point located on the bottom of the surface of the insulating body.

Finally, the connector is soldered to the circuit board using a solder ball that is attached to the soldering points.

It is also known from US-A-4 467 344 to produce an electrical connection by means of a body made of fusible material. Due to a large amount of solder which surrounds the contact pin and occupies a predetermined area in the longitudinal direction of the pin, this method cannot be used in high-density connector arrangements which are produced using the surface mounting technique and have a small distance between the rows and columns of the connectors.

Patent application WO 96/42123, filed by the same applicant, describes components having contacts with a low cross-section and a curved contact tip on which fusible material is applied.

EP 0 591 772 A1 teaches another way of soldering connectors to a multilayer printed circuit board using contact points. However, this teaching is limited to components that do not have contacts arranged in a housing made of insulating material.

US-A 5 495 668 teaches the use of connections between a semiconductor chip and a printed circuit board. The connections are made by means of wires, at the ends of which soldering points are provided. The components are again not arranged in a housing made of insulating material.

US-A 5 131 871 relates to a construction capable of reducing stresses in the connector block in a high-density connector. The walls forming a honeycomb are thin and the invention proposes to reinforce them by means of projections. These projections form supports for a contact, but do not secure it by deformation.

US-A-5 358 417 describes a power connector having a body of insulating material through which a plurality of cables extend. The contacts at the ends of these cables rest on contact pads and the wires of these cables are connected to one another by means of a conductive gel which is capable of keeping the wires and the contact pads in contact with one another without solder balls.

EP 0 782 220-A2 deals with clamping means provided within openings in a body. The clamping means are formed by clamps acting on wires in insulated cables.

Other patents relate to inventions whose aim is to limit the wetting effect during the soldering process. For example, WO 97/45896 teaches a small connector for mobile phones in which the length of the contact between its ends is very small. Since one of the ends serves to receive the solder during a surface mounting process, only a part of this contact has a nickel coating to prevent the solder from creeping.

US-A 3 864 004 describes a circuit board connector socket in which a portion of the spring contact is provided with a solder-repellent coating to ensure that no solder creeps up to the contact spring.

DE PS 3 712 691 also describes a coated contact pin with a nickel intermediate layer as an anti-diffusion barrier.

US-A 5 453 017 describes the use of a layer of non-solderable material as a coating so that solder does not adhere to the long sides of the connector.

While the use of BGA or similar techniques to interconnect integrated circuits to a substrate has many advantages, a suitable means of mounting an electrical connector or similar component to a printed circuit board (PWB) or similar substrate has yet to be developed. It is important in most cases that the surfaces of the solder balls contacting the substrate be coplanar to form a substantially flat mounting surface so that the balls will eventually melt and the solder will be evenly distributed over the printed circuit substrate. Any major deviation in the coplanarity between the solder and a given substrate can result in poor soldering results when the connector is reflowed to a printed circuit board. To achieve high soldering reliability, customers specify very strict coplanarity requirements, typically on the order of 0.004 inches (0.01 mm). The coplanarity of the solder balls depends on the size of the solder balls and their

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positioning on the connector. The final size of the ball depends on the total volume of solder initially present in the solder paste and the solder balls. When applying solder balls to a connector contact, these considerations are particularly challenging because variations in the volume of solder mass received in the connector contact affect the potential variability of the size of the solder mass and thus the coplanarity of the solder balls on the connector at the attachment surface.

Another problem with soldering connectors to a substrate is that connectors often have housings made of insulating material with relatively complex shapes, e.g. those containing a large number of cavities. Residual stresses in such thermoplastic housings can result from the injection molding process, from the formation of stresses as a result of contact insertion, or a combination of both. These housings can be bent or twisted, either originally or after heating to the temperatures required in SMT processes, e.g. the temperatures required to melt the solder balls.

Such twisting or bending of the housing can cause a misfit between the connector assembly and the circuit board, resulting in unreliable soldering because the surface mount elements, such as solder balls, are not sufficiently in contact with the solder paste or are not sufficiently close to the circuit board prior to soldering.

There is therefore a need for the secure and effective connection of high-density electrical connectors to substrates using surface mount technology.

Summary of the invention

Electrical connectors according to the present invention have a high input/output density and provide a reliable connection to circuit substrates through the surface mount technique. These connectors have a high coplanarity on the mounting surface.

Electrical connectors according to the present invention are those in which one or more contacts are connectable to a substrate by a fusible electrically conductive material. This fusible electrically conductive material is a solder mass, preferably comprising a solder ball that is fusible to establish the main current path between the contact and a circuit substrate.

One aspect of the present invention relates to a method of forming an external fusible electrically conductive contact on an element of an electrical connector. According to one method, a recess is formed on the outer side of the connector element or contact. A region of a conductive contact extends from the inside of the connector element into this recess on the outside of the housing. The recess is filled with a predetermined volume of solder paste. A fusible conductive element, e.g. a solder ball,

is positioned in the recess on the outside of the housing. The conductive element in the recess is then heated to a temperature sufficient to melt the solder paste and fuse the fusible conductive element in the region of the contact that projects into the recess.

The invention is also directed to a contact for use in an electrical connector having a contact region in which the contact is connectable to a fusible conductive element, such as a solder ball. A central region of the contact is positioned between the contact tip and the contact region. The central region is designed to resist the flow of molten solder, e.g. by applying a coating of a material not wettable by solder. This arrangement prevents the solder from creeping from the solder ball into the region in which the contact is attached in the housing.

The coplanarity of the surface mounting surface of the connector is maintained by providing an insulating connector housing in which the formation of stresses is avoided. According to this aspect of the invention, a contact is inserted into an opening in the housing. The cross-section of the opening is sized such that at least one of its sides has a projection which is deformable by the contacts when the contact is inserted into the opening. This arrangement avoids the formation of stresses as a result of a plurality of insertions of the contacts, so that distortion or twisting of the housing is minimized.

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Short description of the characters

The method and the connector according to the present invention are explained in more detail below with reference to the drawing, in which:

Fig. 1 is a plan view of a female connector of a preferred embodiment of the connector according to the present invention;

Fig. 2 is a partially sectioned side view of one end of the socket connector of Fig. 1;

Fig. 3 is a plan view of a plug element of a preferred embodiment of the present invention;

Fig. 4 is a partially sectioned side view of one end of the plug element according to Fig. 3;

Fig. 5 is a partially sectioned side view of the socket and the plug element of Figs. 1 to 4 in the non-extended state;

Fig. 6 is a side view of the ends of the socket and the plug element according to Fig. 5 in the mated state;

Fig. 7a, 7b and 7c are sectional end views of the first, second and third phases of mating the socket and the plug element according to Fig. 5;

Fig. 8 the socket shown in Fig. 1 from below before solder balls are attached;

Fig. 9 is a bottom view of the socket connector of Fig. 8 after the solder balls have been placed thereon;

Fig. 10 is a detailed sectional view of area XII in Fig. 1; Fig. 11 is an enlarged view of the section in Fig. 4; Fig. 12 is an enlarged view of the section in Fig. 10; Fig. 13 is an enlarged section along the line 13-13 in Fig. 10;

Fig. 14 is a plan view of a second preferred embodiment of a socket connector according to the present invention;

Fig. 15 is a side view of the edge of the socket connector according to Fig. 14;

Fig. 16 is a plan view of a second preferred embodiment of a connector of the present invention;

Fig. 17 is a side view of the connector according to Fig. 16;

Fig. 18 is a side view of the assembled socket and connector according to Figs. 14 to 17;

Fig. 19 is a plan view of a socket according to a third preferred embodiment of a socket connector according to the present invention;

Fig. 20 is a side view of the socket shown in Fig. 14;

Fig. 21 is a plan view of the plug element according to the third preferred embodiment of a connector according to the present invention;

Fig. 22 is a side view of the plug element according to Fig. 21;

Fig. 23 is a side view of the nested socket and plug according to Figs. 19 to 22;

Fig. 24a and 24b are diagrams in which the temperature is plotted against time and distance during solder reflow according to Examples 1 and 2 of the method according to the invention;

Fig. 25a to 25f show laser-generated profiles of the product according to Example 3 and the process according to the invention;

Fig. 26a and 26b are X-ray photographs showing the product of Example 4 and the process of the invention;

Fig. 26c and 26d are electron micrographs showing the product of Example 4 and the process according to the invention;

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Fig. 27 is a view similar to Fig. 10 with grounding and power contacts omitted;

Fig. 28 is a cross section through XXXI-XXXI in Fig. 13;

Figure 29 is a computer calculated representation of predicted stresses in an insulating housing similar to those shown in the preferred embodiments of the present invention;

Fig. 30 is a diagram in which the contact holding force is plotted as a function of the deformation (compression) of a projection of the insulating housing according to Fig. 27;

Fig. 31 is a plan view of a female signal contact used in a preferred embodiment of the connector according to the invention;

Fig. 32 is a plan view of a plug signal contact used in a preferred embodiment of the connector according to the invention;

Fig. 33 is a plan view of a female ground/power contact with carrier strip used in a preferred embodiment of the connector according to the present invention; and

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Fig. 34 is a plan view of a ground/power contact with transport strips used in a preferred embodiment of the connector according to the present invention.

Detailed description of the preferred embodiments

1 and 2 and 12 and 13, a set of mating connectors according to a first embodiment of a high density connector according to the invention comprises a housing which bears the reference numeral 10. The bottom portion of the housing bears the reference numeral 12. The bottom is preferably manufactured by injection molding a suitable insulating polymer material which can withstand the reflow temperatures of the surface mount process. A suitable material is, for example, a liquid crystal polymer (LCP). The bottom portion includes a bottom wall 14 having an outer side 16 and an inner side 18. On the outer side are arranged outer slots, for example slots 20, 22, 24, 26 and 28 (Fig. 12). On the inner side are arranged inner contact receiving slots, for example slots 30, 32, 34, 36 and 38. These inner and outer slots are separated by central slots, such as slots 40, 42. B. slots 40, 42, 44, 46 and 48. Each of the outer slots has a bottom wall and a side wall, such as bottom wall 50 and side wall 52 (Fig. 12). Each of the inner signal contact receiving slots has a bottom wall and side intermediate walls, such as bottom wall 54 and side walls 56 and 58. Each of the inner ground or power contact receiving slots also has a bottom wall and diagonal side walls, such as bottom wall 60 and side walls 62 and 64. These inner and outer slots described above and the connecting

Middle slots accommodate ground/power contacts or signal contacts.

The ground or power contacts preferably have an upper portion 66 formed from two contact forks 56, 58 and 70. Each of these forks has a tapered portion 72, a contact point 74 and an outwardly diverging or lead-in portion 76. The ground or power contacts also have a central portion 78 which extends through the bottom wall of the housing and a lower portion 80 which opens into the outer slot. A solder ball 82 is fused to the lower portion 80 as will be described below.

Each of the signal contacts (Figs. 12 and 13) has an upper portion 84 which preferably includes a contact projection 86, a lead-in bend 88 and a stiffening rib 90. The signal contacts also have a central portion 92 which extends through the bottom wall of the housing. Each signal contact has a lower portion 98 (Fig. 13) which opens into the outer slot, e.g. slot 22 in Figs. 12 and 13, where a solder ball 100 is fused to the lower portion 98, as explained below. Referring particularly to Figs. 1 and 2, the bottom portion of the housing includes locking elements, such as those designated by reference numeral 102. These locking elements include an upwardly directed tongue 104 which is superimposed on a vertical slot 106 and which has an outwardly directed projection 108. The bottom portion of the housing further includes similar locking elements 110, 112, 114. The housing also includes an upper portion which, in reference

numeral 116 and which rests on the bottom portion. This upper portion has a top wall 118 and a side wall 120. This upper portion is secured to the bottom portion by locking elements, for example indicated by the reference numeral 122. Each of these locking elements has a side wall slot 124 and a U-shaped locking hook extending downwardly from the top wall and spaced from the side wall slot. The tongue 104 fits between the U-shaped locking hook 126 and the side wall slot 124 so as to enable the U-shaped locking hook to latch the outward projection 108 on the locking element 102 of the bottom portion. The upper portion includes similar locking elements 128, 130 and 132 which latch into the locking elements 110, 112 and 114 in the bottom portion, respectively. The upper portion 116 or the base 102 may also include mounting brackets 134 and 136 having mounting openings 13 and 140. Signal contact receiving openings such as opening 142 and opening 144 are also provided on the upper wall 118 of the upper portion 116. These receiving openings are arranged in a plurality of rows corresponding to the rows of signal contacts in the base portion. Between these rows of signal contact receiving openings are elongated ground or power contact receiving slots such as slots 146 and 148. The upper portion 116 forms a mating surface between the housing 10 and the mating connector 150, which is described further below.

In Fig. 3 and 4 and 11, the plug element of the connector is generally designated 150. The plug has an insulating base

en wall 152 and an outer side wall 154. In the side wall
Opposite openings 156 and 158 are provided, and opposite the bottom wall is an open side 160. Protruding from the side of the plug are mounting brackets 162 and 164 with bracket receiving openings 166 and 168, respectively, which are aligned with fastener receiving openings 138 and 140 in the mounting brackets of the housing.

In Fig. 11 you can see on the inside of the bottom wall 152 internal signal contact slots such as slot 170. E-likewise
On the inside of the bottom wall, internal power or ground contact slots, such as slot 172, are provided. Opposite the external slots in the bottom wall
are external signal contact slots, such as slot 144 and
outer power or ground contact receiving slots are arranged like slot 176. The outer and inner signal contact receiving slots and the inner and outer power or ground contact receiving slots are connected to each other by center slots 178 and 180, respectively. Power or ground contacts 182 are mounted in the power/ground contact receiving slots via the center slots 180. Each contact 182 has an elongated inner portion 184, an elongated central portion 186 secured in the bottom wall 152, and an outer portion 188 extending into the slot 176. A solder ball 190 is fused to the portion 188. The outer portion 188 and the solder ball are partially received in the outer slot 176. The connector also includes a plurality of signal contacts 192. These signal contacts each have an inner region 194, a middle region 196 which is located in the bottom wall

and a contact tip 198 which projects into the slot 174. A solder ball 200 is melted onto the contact tongue 198. It can again be observed that the outer region and the solder ball are partially received by the outer slot 170.

As seen in Figures 5 through 7c, the connector described above is mounted on a circuit substrate such as the rigid PWB board 202, and the housing is mounted on a similar PWB board 204. The connector and housing thus form a board-to-board connection as shown in Figure 6. The connector has a two-dimensional array of signal contacts such as 192 having solder balls 200 fused thereto, and a plurality of ground/power contacts such as contacts 192 having solder balls 190 fused thereto. Through the surface mount technique, the solder balls are also soldered to the PWB board 202 to secure the entire connector to the PWB board and to provide electrical contact between the signal contacts and the ground or power contacts in the connector and the PWB board. Although not all contacts are shown in Figure 5, all contacts are connected with solder balls and are also connected to the PWB board in the same manner. Similarly, solder balls 100 are soldered onto the package signal contacts 84 and these solder balls are soldered to the PWB board 204. Package ground/power contacts 66 are mounted in slots 134 and soldered with solder balls 82 and these solder balls are soldered to the PWB board 204.

The connector is aligned with the housing such that the outer side wall 154 of the connector overlaps the outer side wall 120 of the upper portion 118 of the housing.

The interlocking of the plug and housing is seen in more detail in particular in Figures 7a through 7c. Figure 7a shows, after prior alignment, the ground/power contacts in the plug inserted into the ground/power contact receiving slots in the housing and engaging the corresponding ground/power contacts in the housing. The signal contacts inserted into the signal contact slots in the housing. Figure 7b shows the signal contacts in the plug engaging the corresponding signal contacts in the housing and the power/ground contacts in the plug engaging between opposing tabs of the power/ground contacts in the housing. Figure 7c shows the signal contacts in the plug fully engaging the signal contacts in the housing. The power/ground contacts in the plug are positioned at the base of the fork of the power/ground contacts in the housing.

Fig. 8 shows the outside 16 of the insulating bottom 12 of the housing before the solder balls are applied. Before the solder balls are applied, the contact tabs of the signal contacts, e.g. contact tab 82, and the power/ground contacts, e.g. contact tabs 98, are arranged in corresponding outer slots, e.g. outer slots 20, 22, 24, 26 and 28, by inserting the contacts into the opposite side 18 of the bottom 12. A certain amount of solder paste of suitable composition is applied to fill each outer slot in the

Essentially, the solder balls are then placed over the outer or mounting surface of the base.

Preferably, the outer slots are transversely narrower than the diameter of the solder balls so that the solder balls are supported by the edges of the slots in a position near the contact tabs of the contacts. To maximize the stability of the solder balls in the slot, a slot having a round or rectangular cross-section is preferred. The solder paste helps to retain a solder ball in each of the slots, as shown in Fig. 9, where, for example, solder ball 82 is shown in slot 20 and solder ball 100 in slot 22. Additionally, solder balls 230, 232 and 234 are shown resting in slots 24, 26 and 28. The outside of the plug is substantially identical to the outside of the housing before the solder balls are placed, as shown in Fig. 8, and after the solder balls are placed, as shown in Fig. 11. After placement of the solder balls in the outer slots, the connector is subjected to a reflow process to solder the solder balls to the contact tabs. The outer surfaces of the connectors, together with the solder balls, and in particular the outer surface of the solder balls, form a substantially flat mounting surface by which the connector is mounted to a circuit-bearing substrate, such as a PWB board.

10 and 13 show a variant of the embodiment according to Fig. 1, in which, instead of the forked housing contacts 66, opposing pairs of leaf spring contacts 66a, 66b engage in the grounding/power contacts 182.

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14 to 18 illustrate a second preferred embodiment of a set of mating connectors according to the present invention. In FIGS. 14 and 15, this set includes a housing 236. This housing includes an insulative base having an inner side 240 and sides 242 and an outer side 244. The base includes opposing alignment tabs 246 and 248. On the inner side of the housing are contacts 250 and 252, each having portions that bend away from each other and then converge toward a contact point from which they diverge again. Contacts 251 are mounted on the base 231 in the same manner as in the embodiments shown in FIGS. 1 to 13. Solder balls, such as solder ball 254, are mounted on the board-facing side of contacts 250 and 252 as described above. 16 and 17, the kit also includes a plug 258 having an insulative base 260 having an inner side 262, an outer side wall 264, and an outer side. At one end of the base are a pair of vertical end walls 268 and 270 having a central end slot 272. At the opposite end of the base are another pair of end walls 274 and 276 having a central end slot 278. Starting from the inner side of the base are a plurality of contacts, such as contact 280 extending from slot 282. A solder ball 284 is fused onto each of these contacts. These contacts are offset from one another. For example, contact 286 is offset from contact 280 so that rows of contacts can be placed closer together to increase contact density. Fig.

shows that each contact, such as contact 280, is perpendicularly aligned with one of pairs of converging contacts, such as contacts 250 and 252, in the housing and is disposed between converging contacts. It can also be seen that alignment tabs 246 and 248 engage slots 272 and 278 in the plug. In this embodiment, the separate ground/power contacts used in the embodiment shown in Figs. 1-13 are not present. Such functions can be incorporated into undivided contact pairs if desired.

19 through 23 show a third preferred embodiment of a set of mated connectors. The plug is designated 290. This plug includes a socket 292 having a bottom wall 294 and an outer side wall 296 and opposing alignment tabs 298 and 300. The bottom wall of the socket has an inner side 302 and an outer side 304. Signal contacts, such as contact 306, extend from the inner side 302. The signal contacts are also staggered in alternating rows to increase contact density. The plug also includes ground or power contacts 310, 312, 314 and 316 disposed adjacent each of the sides of the plug parallel to one side of the side wall. On the outer side of the bottom wall, signal contact solder balls such as solder ball 318 and power/ground contact solder balls such as 320 are soldered to their respective contacts in the same manner as described with respect to the first embodiment. The housing is designated 322 and includes an insulating base 324 having a bottom wall 326, an outer side wall 328 and slots 330 and 332 for receiving the alignment projections.

The bottom wall has an outer side 334 and an inner side 336. Signal contacts such as contacts 338 and 340 extend from the inner side. The contacts in adjacent transverse rows are also axially offset from one another, allowing for increased contact density. Parallel to each side of the peripheral wall are lateral power or ground contacts 324, 344, 346 and 350. On the outer side of the bottom wall, a solder ball such as solder ball 252 is provided for each signal contact. Solder balls such as at 354 are also provided for securing each power or ground pin. As can be seen in Fig. 23, the plug 290 engages the housing 322.

As previously mentioned, components such as electrical connectors mounted on circuit substrates by surface mount techniques must meet very demanding coplanarity specifications. If tight coplanarity tolerances, typically on the order of about 0.003 to 0.004 inches (0.0075 to 0.01 mm), are not met, manufacturers experience undesirably high scrap rates due to poor solder joints. Variations in the distance of a portion of the surface mount contact from the circuit substrate can result from variations in the location of the contact in the insulating housing, which occurs as a result of contact insertion, and from deformation of the housing, which results in bending or twisting of the mounting surface of the connector body. Connectors according to the invention are able to meet the stringent coplanarity requirements by carefully arranging and sizing the fusible bodies. These fusible bodies are used to

used to bond the connector to a substrate. The stringent coplanarity requirements are also met by the use of contact securing arrangements that prevent stress accumulation in the connector housing that can distort that housing.

In the embodiments of Figures 1 to 23, the metal contacts are mounted in insulating housings in a manner which seeks to avoid the introduction of mechanical stresses in the housing body. This is accomplished by the use of specially shaped slots or openings into which the securing portions of the contact are inserted. In an arrangement which is particularly useful in small signal contacts, the slot has a size substantially equal to the size and shape of all but one of the surfaces of the contact. The wall of the slot opposite that one side has an injection molded side projection which projects into the slot. The distance between the distal end of the projection and the opposite wall of the slot is less than the thickness of the contact.

Thus, the distal portion of the projection is contacted and deformed by the contact as it is inserted into the slot. The contact is held securely in the slot by the perpendicular force exerted on the contact by the deformable projection. Since the distal end of the projection is deformable, stress build-up in the housing is avoided. In the preferred embodiments shown, the projections are in the form of a pyramidal rib integrally formed on one of the side walls of the slot.

The particular rib shape shown here is believed to be optimum for the particular package in which it is used, but other similar ribs of slightly different shape or size may be used to advantage with other package types. In Figs. 27 and 28, a signal contact 494 is supported in a slot 496 and abuts against a rib 498. The rib has a flat surface 500 where it contacts the contact 494 and opposing sloped sides 502 and 504. The contact 494 is securely held in the slot by the engagement of rear and side edges of the slot 496 and the rib 498. The region of the rib adjacent to the surface 500 is freely deformable as the contact 494 is pressed into the slot 496, avoiding any stress that might be induced by the insertion of the contact.

Similarly, a power/ground contact is supported in slot 508 and presses against deformable rib 510. The rib has a distal region 512 where it presses against the contact and opposing slanted sides 51 and 516. In this arrangement, there is also an opposing rib, such as rib 518. This opposing insulating rib also has a distal region 520 and slanted sides 522 and 524. The opposing deformable ribs can be used to support larger contacts and to center the contact in the slot.

The person skilled in the art will recognize that the exact shape, size, number and arrangement of such ribs for different types of housings

can vary, these factors being chosen to isolate as much as possible stresses in the housing in the deformable ribs. Fig. 29 is a graph generated using ANSYS Stress Analysis software from Ansys, Inc., Houston, Pennsylvania, showing that by using a contact securing arrangement according to Figs. 27 and 28, high stress levels in the ribs are isolated and substantially do not extend beyond the contact mounting slots, significantly reducing the risk of warping or twisting of the housing which could result from the large number of contact entries. The units of the stress change ranges shown in Fig. 29 are N/mm ² and mm is the unit of displacement shown. Fig. 30 shows that for a typical contact 494, increases in the deformation (compression) of the distal portion of the deformable rib up to about 0.0004 inches (0.001 mm) resulted in an increasing retention force between the contact and the housing caused by the normal force exerted on the contact by the rib. After 0.0004 inches (0.001 mm) of deformation (compression), only small increases in retention force occurred.

As previously mentioned, other factors also affect the coplanarity of the substrate mounting surface of a connector using surface mount techniques. These include the uniformity of the size of the solder balls and the location of the solder balls with respect to the mounting surface of the connector housing. In the preferred embodiments described above, the contact tongue of each contact is disposed in a slot. The outer slots are substantially the same size and

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shape. These slots have several important properties related to the present invention. The slots can accommodate a highly accurate equal amount of solder paste, e.g. by a simple apply and wipe technique. Thus, the amount of solder paste available to secure each solder ball to the contact is substantially equal. The slots locate the location of each solder ball in the lateral X-Y direction before the solder balls are secured to the contacts. The slots also locate the solder balls in the Z direction relative to the bottom surface of the housing and the distance of the solder balls from the contact tabs of the contact. The nominal extension of the tab in the slot is chosen such that, with maximum tolerance of the extension of the tab into the slot, the tab does not contact the solder ball and thus affect its location in the Z direction. The melting of the solder ball on the contact tongue is ensured by the presence of a relatively equal and adequate amount of solder from the solder paste in the slot. Any variations in the distance between the contact tongue and the solder ball are compensated by the variable volume of solder paste in the slot.

In order to have an adequate amount of solder near the solder ball during the reflow step used to attach the solder balls to the contacts and to avoid solder creep on the attachment surfaces of the contact, the contact is treated to prevent solder creep. In Fig. 31, contacts 526 and 528 are shown hanging from a transport strip 530. The contacts have a contact engagement area 532 which is normally coated with non-oxidizing

· * · · · · • • · ···· • • • · • » •

metals such as gold, palladium or a palladium alloy. The contacts also have a central region 534 which forms the contact mounting area in the housing. An "anti-solder creep" or non-solder wettable material is applied to the central region 532 of the contact. A preferred material for this purpose is a nickel plating. Without intending to be bound by any particular theory, it is believed that the solder resistant property of these nickel coated regions results from or is enhanced by oxidation of the nickel after plating, e.g. by exposure to ambient air for several days. Surprisingly, it has been found that the nickel or nickel oxide barrier prevents or reduces solder creep in such contacts. In order for the nickel or nickel oxide plating to perform such a passivation function, it is preferred that the plating have a thickness of 10 μm. to 100 μηιδια (25 to 250 μηι), and preferably around 50 μηιδια (125 μηι). Other solder creep resistant materials also appear to be useful for this purpose, such as fluorines which contain solder resistant coatings. These may be particularly useful when the entire contact is coated with a continuous outer layer of a solder wettable material, e.g. gold. The contact tip region 536 may preferably be coated with a solder accepting material such as gold, tin or tin alloys. Preferably, the entire contact is coated with nickel. Precious metal layers are then selectively deposited on the upper region over the nickel. This noble metal coating in the upper region preferably has a thickness between 10 μm to 100 μm (25 μm to 250 μm) and preferably 30 μm (75 μm). In the lower region

a solder wettable metal layer is selectively deposited. Alternatively, an electroplated layer of chromium may be used in place of the nickel layer. Figure 32 shows plug signal contacts 538 and 540 suspended from a transport strip 542. Each of these contacts has a gold plated tongue portion 544, a nickel plated center attachment and anti-creep portion 536, and a precious metal plated mating portion 548. Similarly, Figure 33 shows ground/power contact 550 suspended from a transport strip 552. This contact has a gold plated lower tongue 554, a nickel plated center "anti-creep" portion 556, and a gold plated contact mating portion 558. Another feature of ground/power contact 550 which also reduces creepage is a series of holes in tongue portion 554, such as holes in the center of the tongue portion 554. 34 shows a plug ground/power contact 568 having a lower gold plated tongue portion 570, a nickel plated middle "anti-creep" portion 572, and an upper gold plated portion 574. The ground/power contact 568 does not have a separate transport strip, but rather has openings, such as opening 576, which allow the contact itself to perform this transport function. In any of the contacts described above, the gold in the lower portion can be replaced with tin or other solder wettable material. In all of the contacts shown in FIGS. 31-34, the width of the lower gold plated tongue portion, such as slot 566, is 100mm. B. in Fig. 34 shown at wi, preferably between 0.1 mm to 0.25 mm. The width of the

Nickel coated middle region, designated W2 in Fig. 34, is preferably between 0.1 mm to 1 mm.

In the method according to the invention, the conductive element is preferably a solder ball. However, the person skilled in the art knows that it is also possible to use other fusible materials that have a melting temperature that is lower than the melting temperature of the insulating body. The fusible element can also have a shape other than a ball. The solder ball or other conductive element preferably has a diameter that is 50% to 200% larger than the width of the gap. This diameter is preferably dependent on the depth of the gap and the width of the gap corresponds to between 50 and 200% of the depth. The volume of the solder ball is preferably between 75 and 150% of the volume of the gap and particularly preferably it has approximately the same volume as the gap. The contact tongue extends sufficiently deep into the gap to provide a sufficient surface for the solder ball to be soldered thereto and preferably extends into the gap between 25 and 75%, more preferably up to 50% of the depth of the gap. The gaps may have a round, square or any other rectangular cross-section. When the conductive element is solder, it is preferably an alloy of about 90% tin and 10% lead to about 55% tin and 45% lead. Preferably it is a eutectic alloy of 63% tin and 37% lead with a melting point of 183°C. Typically a "harder" solder alloy with a higher lead content is used to match materials such as ceramics. The "hard" solder ball will "mushroom" if it

softens under typical surface mount conditions, but it will not melt. A "soft" eutectic ball is used for attachment to PCB boards and will usually melt and deform under typical surface mount conditions.

Other types of solder suitable for electronic applications also appear to be suitable for this process. Such solder materials include, but are not limited to, electronically acceptable tin antimony, tin silver, lead silver alloys and indium. Before the solder ball or other conductive element is positioned in the gap, this gap is usually filled with solder paste.

Alternatively, instead of a solder ball as described above, a body of a material which is not fusible at surface mount temperatures may be used and secured to the contacts by melting the solder paste in the gaps. The connector mounting surface comprises a plurality of non-fusible balls in a strictly coplanar matrix. Such a connector would be secured to a substrate by a conventional surface mount technique. While it is believed that any solder paste or cream containing conventional organic or inorganic solder fluxes is useful for this process, a non-pure solder paste or cream is preferred. Such solder pastes or creams contain a solder alloy in the form of a fine powder suspended in suitable flux material. This powder is usually an alloy and not a mixture of ingredients. The ratio of the solder

to flux is usually in the range of 80 to 95% by weight of solder, or approximately 80% by volume of the solder. A solder cream is prepared by suspending solder material in a flux resin. Preferably, the flux resin is white resin or a weakly active flux resin, although activated or hyperactivated resin may be used for various purposes. A solder paste is prepared by suspending a powdered solder alloy in an organic flux acid or an inorganic flux acid. Such organic acids may be selected from lactic acid, oleic acid, stearic acid, phthalic acid, citric acid, or similar acids. Inorganic acids may be selected from hydrochloric acid, hydrofluoric acid, and orthophosphoric acid. The cream or paste may be applied by brushing, screen printing, or by extrusion onto the surface, which is preferably slightly preheated to ensure good wetting. Although it has been found that the creep of solder onto the contact is significantly reduced when a solder paste or cream is used, it is believed that a solder flux paste alone can be used as well if a suitable passivating agent is used. Such suitable passivating agents may include fluorides having solder resistant coatings such as FLUORAD, which is available from 3M Corporation.

The heating is preferably carried out in a panel infrared solder melting belt oven. The solder element is usually heated to a temperature between 183° to 195° C. However, depending on the housing material, solder materials with different melting temperatures can be used. The belt oven is

preferably operated at a belt speed of 10 to 14 inches/s (25 to 35 cm/s), with the belt being passed through a plurality of successive heating phases in a total time of about 5 to 10 minutes. Prior to introduction into the belt oven, the connector housing, contacts and solder elements may be preheated to a high temperature and for at least 1 hour. A temperature profile is established in the belt oven based on an appropriate peak temperature, maximum temperature rise and time above the melting temperature. The peak temperature is the highest temperature reached by the housing. For a solder element with a melting temperature of 183° C, the peak temperature would typically be between 185° C and 195° C. The maximum rise is measured in ⁰ C/s and determines how quickly the connector housing temperature can change so that warping or twisting is prevented. For most applications of this process, a maximum initial temperature rise of 2° C/s to 15° C/s is preferred. After the melting point of the solder is reached, the temperature decrease is preferably between -2° C/s and -15° C/s. An important aspect of the method according to the invention is that the time above the melting temperature is minimized. The time above the melting temperature is a measure of how long the solder element remains in its liquid phase. It has been found that if the time the solder is in its liquid phase is minimized, creep of the solder from the gap at the contact is highly eliminated or significantly reduced. A preferred rise time for the temperature measured on the board is between 180° C and 200° C and the fall time for the temperature measured on the board is between 200 and

180° C, both are between 10 s to 100 s. Without wishing to be limited to any particular theory, it is believed that during these relatively short periods of time, surface tensions of the liquid solder element prevent the liquid solder from flowing through the contact slot in the bottom of the slot. After such periods, however, the liquid solder will flow through the contact slot and wet the contact. Before bringing the temperature of the solder element to its melting temperature, it may also be advantageous to initially operate at a high temperature increase rate before the melting temperature is reached and to reduce the temperature increase rate or the temperature decrease rate and then continue operating at a high temperature increase rate until the melting temperature is reached. Selecting a suitable housing material can also improve results. Preferably, the housing material is a fully aromatic liquid crystal polyester (LCP) with properties such as high glass transition temperature, low thermal coefficient, low moisture absorption and high fracture strength, with good flow properties and low viscosity, high melting temperature and high flash point.

The process according to the invention is further explained below with reference to the following example.

example 1

An insulating base for a connector plug and a housing are described above with reference to Figs. 1 to 18. Contacts in the

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The contacts were positioned in the socket as described. These contacts were made of beryllium copper and plated with gold over their entire surface to a thickness of 30 μηι. The socket material was a DUPONT H6130 liquid crystal polymer (LCP). The length and width of the plug were 52.5 mm (including the mounting clips) and 42.36 mm. The slots on the outer surface of the plug and the container housing were square in cross-section with an edge length of 0.62 mm and a depth of 0.4 mm. Approximately 0.2 mm of the contact extended into the slot. Other dimensions were generally in proportion to the dimensions mentioned above in accordance with Figs. 1 through 18. On the outsides of the plug and housing, the slots were filled or substantially filled with CLEANLINE LR 725, a non-pure solder cream commercially available from Alphametais Inc., Jersey City, New Jersey. The plug and housing were placed with their outsides over the specified amount of spherical solder balls so that one solder ball was embedded in each slot. The solder balls used were ALPHAMETAL no flux 63SN/37PB spherical solder balls having a diameter of 0.030 inch ± 0.001 inch (0.075 mm ± 0.025 mm) and a weight of about 0.00195 g. The plug and housing were treated with FLUORAD, an "anti-solder creepage material" available from 3M Corporation. After such treatment, the plug and housing were dried in a convection oven for 2 hours at 105°C. The plug and housing were then mounted on separate circuit boards made of conventional reinforced epoxy circuit board material with a thickness of 0.061 inch (0.153 mm). As can be seen in Fig. 9, a thermocouple was mounted on the outside of the plug at

at location T. Another thermocouple was placed in the center of the carrier surface of the circuit board opposite the connector. The connector and housing were then processed in the panel infrared solder reflow belt oven. As is typical for this type of oven, the connector and housing were moved through six zones in the reflow oven. The belt speed was 13 inches/min (32.5 cm/min). The heating temperatures in each zone are shown in Table 1. The minimum and maximum temperatures for the connector and for the carrier board are shown in Table 2. The positive and negative rates of temperature change are shown in Table 3. The rise time and fall time measured on the circuit board between 180° C and 200° C are shown in Table 4. Fig. 24b shows the temperature versus time and versus distance for the connector where the bold line is the temperature at the thermocouple on the carrier board and the thin line is the temperature at the thermocouple on the outside of the connector. Visual observation of the plug and housing after solder reflow showed that almost all of the solder balls on the contact terminals had reflowed into their respective slots. The solder ball heights over the outer surfaces of the plug and housing also appeared relatively uniform. There was no noticeable warping or twisting of the housing.

Example 2

Another connector and housing were prepared in substantially the same manner as described in Example 1, and solder balls were placed on the outside of the slots.

Several hours after treatment in the solder reflow oven of Example 1, under slightly different atmospheric conditions, another connector and housing substantially similar to those used in Example 1 were subjected to a similar reflow heating as in Example 1. The oven conditions are shown in Table 1. Minimum and maximum temperatures of the connector and the adjacent carrier plate are shown in Table 2. The maximum increase and decrease rates are shown in Table 3, and the rise time and fall time measured on the plates between 180° C and 200° C are shown in Table 4. Fig. 24b shows the temperature versus time and versus distance. It can be seen that the curve shown in Fig. 24b looks slightly different from that in Fig. 24a, the difference being attributed to the different atmospheric ambient conditions. Visual observation of the resulting connectors showed similar results to those obtained in Example 1.

BE #1 .äs": ·: •
· · · · ·
* · · · ·
*··· ·· ·* RICH TABLE 1 upper 350 Temperature (° C) #2 #3 #4 #5 AT GAME un- 275 230 31( 1

1 lower unge unge heats heats 2 upper 350 unge heats 2 lower unge unge heats heats

275 230 310

275 230 310

275 230 710

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unheated unheated unheated unheated

TABLE 2

INTERCONNECTS Time PLATE Time AT maximum (min & s) maximum (min & s) GAME temperature temperature ( ⁰ C) 4:37.6 ( ⁰ C) — 1 188 — — 4:19.8 1 — 4:53.2 232 — 2 191 — 5:10.4 2 —_— 229

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TABLE 3 Positive and negative maximum change ° C/s

INTERCONNECTS achieved time PLATE achieved time AT maximum (min & s) maximum (min & s) GAME 0:50.4 0:30.4 1 +2 6:45.2 +2 5:58.8 1 -2 7:08.0 -3 1:14.8 2 +3 6:13.8 +3 6:14.0 2 -15 -7

TABLE 4 Rise time and total time between 180° C and 200° C

(measured on the plate)

EXAMPLE RISE TIME SINKING TIME (min & s) (min & s) 1 0:28.8 0:15.2 2 1:31.6 0:40.6 Example 3

Another connector was manufactured under essentially the same conditions as described in Examples 1 and 2, except that the specific curves shown in Figures 24a and 24b were slightly different due to atmospheric conditions. After completion of this connector,

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In turn, the solder balls were examined at six locations on the outer surface of the plug with a Laser Point Rang Sensor (PRS) available from Cyber Optics Corporation of Minneapolis, Minnesota. Fig. 9 shows that these locations are designated as regions 25a and 25b when the laser originated from location L1, regions 25c and 25d when the laser originated from L2, and finally regions 25e and 25f when the laser originated from L3. In all of these regions, a laser profile of the contour of the five solder balls in each of these regions was made. These laser profiles are reproduced in Figs. 25a through 25f. The height of each of these solder balls at its highest point above the plane of the outside of the plug is shown in Table 3. For each of these groups of solder balls, the one closest to the face of the connector of Fig. 9 was considered as the first position in Table 5, which is the left-hand solder ball of the illustrations in Figs. 25a to 25f. Examination of the results shows that in each group of five solder balls there was an acceptable degree of uniformity in the height of the solder balls.

1 TABLE 5 3 4 5 18.1 Height (0.001 inch) 19.5 19.6 19.1 GROUP 19.2 2 17.6 18.5 18.0 25a 20.4 18.9 21.6 21.1 21.4 25b 19.9 18.5 20.1 21.2 20.5 25c 18.2 21.1 19.3 18.2 18.7 25d 19.1 20.1 19.0 18.2 18.9 25e ITIL ····
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Example 4

Another connector was manufactured under substantially the same conditions as described in Examples 1 and 2 except for the specific curves of Figures 24a and 24b due to different atmospheric conditions. In almost all cases, the solder balls were satisfactorily reflowed onto the contact terminals and the solder balls were at an acceptably uniform height above the plane of the outer surface of the plug and housing as determined by visual inspection. A stencil having a pattern corresponding to the arrangement of the solder balls on the plug and housing was used to apply solder paste to conductive solder pads on two different printed circuit boards having a thickness of 0.61 inches (0.153 mm). The plug was positioned on one printed circuit board and the housing on the other. The plug and housing were then heated separately in the conveyor furnace under conditions similar to those used to reflow the solder balls on the contacts except that the conveyor speed was reduced to 11 inches/sec (27 cm/sec). After cooling, the plug and housing were found to be satisfactorily soldered to their respective plates. Figures 26a and 26b show X-ray photographs of selected solder balls. Cross-sectional electron micrographs were taken to show the reflow of the solder balls on the signal contact terminals. These electron micrographs are shown in Figures 26c and 26d. There was only one short between adjacent signal contacts.

and good connections were made between the contacts and the solder balls and between the solder balls and the circuit boards at all other points.

In the foregoing, an electrical connector and a method of manufacturing the same have been presented in which the connector can be mounted on a PWB board using surface mount technology. Surprisingly and unexpectedly, it has also been found that a surprisingly high degree of uniformity in the profiles of the solder balls and in particular in their weights and/or volumes occurs.

While the present invention has been described in connection with preferred embodiments shown in the various figures, it is to be understood that similar embodiments with modifications and additions may be used to accomplish the same functions without departing from the scope of the invention. The described arrangements may also be used with respect to components other than connectors having housings of insulating material and carrying elements to be soldered to a PWB or other electrical substrate.

Therefore, the invention should not be understood as being limited to a single embodiment but as defined by the claims.

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·

Claims (7)

1. A high-density electrical connector for mounting on the surface of a substrate having a bottom portion of insulating material ( 12 ) with a plurality of openings and a plurality of contacts connectable to the substrate by a fusible, electrically conductive material, characterized in that each opening has an outer gap ( 20 , 22 , . . ., 28 , 174 , 176 ) and an inner gap ( 30 , 32 , . . ., 38 , 170 , 172 ) connected by a central slot ( 40 , 42 , . . ., 48 , 178 , 180 ). 2. A high density electrical connector according to claim 1, characterized in that each of the inner and outer slots has base and side walls which, together with the central connection slot, receive signal and ground/power contacts. 3. A high-density electrical connector according to claim 1 and 2, characterized in that the fusible, electrically conductive material is a solder ball partially received by each outer gap. 4. High-density electrical connector according to claims 1 to 3, characterized in that the outer gaps define the x, y position of each solder ball before its attachment to the corresponding contact. 5. High-density electrical connector according to claims 1 to 4, characterized in that the solder ball is an external fusible, electrically conductive element. 6. A high-density electrical connector according to claim 1, characterized in that the shape of the gaps is a regular polygon. 7. A high-density electrical connector according to claim 1, characterized in that the gaps have a round shape.