WO2006031097A1

WO2006031097A1 - Shielded interconnection soldering method

Info

Publication number: WO2006031097A1
Application number: PCT/NL2004/000638
Authority: WO
Inventors: Mark Ruiter
Original assignee: Stichting ASTRON
Current assignee: Stichting ASTRON
Priority date: 2004-09-14
Filing date: 2004-09-14
Publication date: 2006-03-23
Anticipated expiration: 2007-03-14

Abstract

With the aid of a first solder mask (30), a first solder material (34) is soldered to a first end surface (11) of a first component (10). After soldering, the first solder material comprises signal conductor solder material (35) soldered to a first signal conductor end (14) of the first component, and signal shield solder material (36) soldered to a first signal shield end (15) of the first component. The first solder material is applied in passageways (32, 33) through the first solder mask (30), which passageways are shaped such that, after soldering, the signal shield solder material (36) comprises, in a plane (M) substantially parallel to the first end surface (11), at least one elongated part (P) of which the longitudinal direction (L) has at least a component which is tangential with respect to a reference point (C) at the signal conductor solder material (35).

Description

Title: Shielded interconnection soldering method

TECHNICAL FIELD AND BACKGROUND ART

The invention relates to a shielded waveguide interconnection soldering method according to the preamble of claim 1. The invention also relates to a first component with an interconnection means soldered to it by means of such soldering method. The invention further relates to an assembly of such first component and a second component. The invention further relates to a solder mask for use in such soldering method.

It is remarked that, within the scope of the invention, the expression "interconnection means" refers to (part of) the means that interconnects different components in a condition in which these components are interconnected.

A soldering method for making a shielded waveguide interconnection between different components is known from practice. By this known method, planar circuits are interconnected with one another, or connected to other components, by using the so-called Ball Grid Array method (BGA). In the BGA a two-dimensional equidistant array of high temperature solder balls is attached to a like array of electrical pads on a planar circuit, using a lower temperature solder. The obtained shielded waveguide interconnection means is formed by a 3 x 3 square portion of the two- dimensional array of solder balls. The solder ball in the center of said square portion functions as the signal conductor of the shielded interconnection means, while the surrounding solder balls of said portion together function as signal shield. This known BGA-based soldering method provides a low-cost way of making a shielded interconnection. However, a drawback of this known method is that the shielding effect achieved by the surrounding solder balls is insufficient, especially for higher electromagnetic frequencies.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a shielded waveguide interconnection soldering method which provides a low-cost way of making an improved shielded solder interconnection. According to the invention this object is achieved by providing a shielded waveguide interconnection soldering method according to claim 1.

As compared to the known soldering method, the method according to the invention substantially only requires modifications to the solder mask and, accordingly, to the way of applying the solder material in passageways through the solder mask. Since these modifications are not particularly complex, the method according to the invention is low-cost. Furthermore, since the longitudinal direction of the elongated part of the signal shield solder material has a component which is tangential with respect to the signal conductor solder material, the shielding effect that will be achieved by the signal shield solder material of the method according to the invention will be improved over the shielding effect achieved by the surrounding solder balls of the known soldering method.

According to the invention there is further provided a first component according to claim 8, an assembly according to claim 9 and a solder mask according to claim 10. Specific embodiments of the invention are set forth in the dependent claims.

Further features, effects and details of the invention appear from the detailed description in which reference is made to examples of methods according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. IA schematically shows a side view of an example of a first component comprising a first end surface provided with a first shielded waveguide end;

Fig. IB schematically shows an upper view of the first component of Fig. IA;

Fig. 1C schematically shows a side view of an example of a second component comprising a second end surface provided with a second shielded waveguide end;

Fig. ID schematically shows an upper view of the second component of Fig. 1C;

Fig. 2A schematically shows an upper view of an example of a solder mask for use in a method according to the invention; Fig. 2B schematically shows a cross section of the solder mask of

Fig. 2A, taken along the line HB of Fig. 2A.

Figs. 3A-3I schematically show some stages in a method according to the invention;

Fig. 4A schematically shows a perspective view of an example of solder material, after being soldered in a method according to the invention;

Fig. 4B schematically shows a cross section of the solder material of Fig. 4A.

Figs. 5A-5F schematically show in cross section some other examples of solder material, after being soldered in a method according to the invention; Fig. 6 schematically shows a perspective view of another example of a solder mask for use in a method according to the invention.

MODES FOR CARRYING OUT THE INVENTION Reference is first made to Figs. 1A-1D. Figs. IA and IB show a first component 10 comprising a first end surface 11 provided with a first shielded waveguide end 12, which comprises a first signal conductor end 14 and a first signal shield end 15. Figs. 1C and ID show a second component 20 comprising a second end surface 21 provided with a second shielded waveguide end 22, which comprises a second signal conductor end 24 and a second signal shield end 25.

The first and second components 10 and 20 may for example be integrated circuits, electronic packages, printed circuit boards, electronic connectors, test fixtures or the bike. The first and second shielded waveguide ends 12 and 22 are ends of shielded, for example coaxial, waveguides (not shown) in the components 10 and 20. The waveguide ends 12 and 22 may for example comprise shielded electrical pads which are electrically connected to conductors or electrically conductive vias in the components 10 and 20. In the shown example, the first and second signal conductor ends 14 and 24 have disk shapes, while the first and second signal shield ends 15 and 25 have flat ring shapes.

In this example, the shielded waveguide is a coaxial waveguide. The centers of the (disk shaped) conductor ends 14, 24 and the shield ends 15, 25 coincide. However, the shielded waveguide may likewise be of a different kind and, for example, include conductor ends which are not positioned in the center of the shielded ends.

Next, examples are described of methods according to the invention for making soldered interconnections for shielded waveguides. Firstly, with reference to Figs. 3A-3D and Figs. 2A-2B, a method is described for making a waveguide interconnection means which is soldered to the first shielded waveguide end 12 of the first component 10 of Figs. IA and IB. Secondly, with reference to Figs. 3E-3I, an elaboration of such method will be described in which the soldered waveguide interconnection means is connected to the second shielded waveguide end 22 of the second component 20 of Figs. 1C and ID.

Fig. 3A shows, in side view, the first component 10 of Figs. IA and IB. In the shown example, it is assumed that the first signal conductor end 14 and the first signal shield end 15 of the first shielded waveguide end 12, are electrical pads. Furthermore, the first component 10 comprises an array of disk shaped electrical pads 16, which are located at the first end surface 11 and arranged in a two-dimensional equidistant grid outside the range of the surface 11 where the first shielded waveguide end 12 is located. In a step of a method according to the invention a first solder mask, such as the first solder mask 30 shown in Figs. 2A and 2B, is positioned over the first end surface 11 of the first component 10. The first solder mask 30 comprises an array of cilindrical passageways 31 through it, which array is designed to match the array of pads 16 at the first end surface 11 when the mask 30 is positioned over the end surface 11. By this matching each passageway 31 ends at a pad 16. As shown in Fig. 2A the mask 30 further comprises a number of differently shaped passageways 33 through it. In the shown example this number is four. In this example, each of these passageways 33, in an upper view of the first solder mask 30, is a sector of an imaginary ring shaped passageway through the mask 30. In the center of such imaginary ring the mask 30 comprises a cilindrical passageway 32 through it. The passageways 32 and 33 are designed such that, when the mask 30 is positioned over the end surface 11, the passageway 32 ends at the first signal conductor pad 14 and the passageways 33 end at the first signal shield pad 15. The passageways 31 may have any suitable cross-sectional shape. The cross- sectional shape of the passageways 31 may or may not be the same as the shape of the pads.

Fig. 3B shows the situation in which the mask 30 is positioned on top of the first end surface 11 of the first component 10, wherein it is assumed that the passageways 31, 32 and 33 are in line with the electrical pads 16, 14 and 15, respectively. Fig. 3B further shows first solder material 34 which, in a further step of the method, has been inserted into the passageways 31, 32 and 33. Such insertion of the first solder material 34 can for example be carried out by wiping soft solder material 34 over the mask 30, wherein excess solder material 34 can for example be removed by moving a suitable beam along the free surface of the mask 30.

In a next step of the method, the mask 30 is lifted up, leaving behind the first solder material 34 on the pads 14, 15 and 16 as shown in Fig. 3C. It is remarked that different suitable materials can be used for the solder material 34, for example 90/10 Pb/Sn added with a suitable flux, as known in the art. In a further consecutive step of the method the first solder material 34 is hardened, for example in a reflow oven, as known in the art. For said material of the first solder material 34, a suitable heating temperature of the reflow oven is for example 250 degrees Celcius. Fig. 3D shows the hardened solder material 34 after thus being soldered to the pads 14, 15 and 16. As shown in Fig. 3D, this hardened solder material 34 comprises signal conductor solder material 35 soldered to the first signal conductor end 14, and signal shield solder material 36 soldered to the first signal shield end 15. Reference is now made to Figs. 4A and 4B. Fig. 4A shows a perspective view of a part of the soldered assembly of Fig. 3D. In the figure, the disk shaped pad 14 as well as part of the ring shaped pad 15 are shown, with the signal conductor solder material 35 and one part of the signal shield solder material 36 soldered to these respective pads. In the figure, broken lines on the solder materials 35 and 36 indicate the location of a plane M which is substantially parallel to the first end surface 11.

Fig. 4B shows a cross section of the solder materials 35 and 36 in the plane M. In this plane M the signal conductor solder material 35 is a circular disk having a center point C. Furthermore, in the plane M the part of the signal shield solder material 36 shown in Fig. 4A, is an elongate part P having a longitudinal direction denoted by L. As can be seen from Fig. 4B, the longitudinal direction L in this example is tangential with respect to the center point C of the signal conductor solder material 35. Advantage over signal shield solder materials not having such elongate part or not having elongate parts with such tangential direction component, is that the electromagnetic shielding will be improved because of the additional tangential shielding. Said advantage is also achieved when the longitudinal direction L, instead of itself being tangential with respect to the center point C, at least has a component which is tangential with respect to the center point C of the signal conductor solder material 35. Furthermore, it is remarked that said advantage is also achieved when (a component of) the longitudinal direction L, instead of being tangential with respect to the center point C, is tangential with respect to another arbitrary reference point at the signal conductor solder material 35. Next, a method for connecting the signal conductor solder material 35 and the signal shield solder material 36 to a second shielded waveguide end of a second component is described. Fur this purpose, reference is now made to Figs. 3E-3G, which show the second component 20 of Figs. 1C and ID with its second end surface 21 provided with the shielded pads 24 and 25. Further, in this example the surface 21 comprises an array of disk shaped electrical pads 26, similar to the array of pads 16 of the first component 10. In the method according to the invention, a second solder mask 40, similar to the first solder mask 30, is positioned on top of the second end surface 21 of the second component 20. This positioning, shown in Fig. 3F, is similar to the positioning of the first solder mask 30 on top of the first component 10. A second solder material 44 is applied in passageways through the second solder mask 40 in a similar way as the first solder material 34 was applied in the passageways through the first solder mask 30. By lifting up the mask 40, the second solder material 44 is left behind on the pads 24, 25 and 26, as shown in Fig. 3G. In a yet further step of the method, the first component 10 is positioned over the second component 20, or vice versa, in such way that the first end surface 11 of the first component 10 is facing towards the second end surface 21 of the second component 20 and in such way that the hardened solder material 34 contacts the second solder material 44. This is shown in Fig. 3H. The assembly shown in Fig. 3H is then placed in the reflow oven and heated to a temperature which is high enough to melt the second solder material 44 and which at the same time is low enough to prevent melting of the first solder material 34. For that purpose, the second solder material 44 is different from the first solder material 34 and is chosen to have a lower eutectic melting point than the first solder material 34. If, for example, 90/10 Pb/Sn, added with a suitable flux, is used for the first solder material 34, a suitable material for the second solder material 44 can for example be 60/40 Pb/Sn, added with a suitable flux, as known in the art. For this second solder material 44 a suitable temperature to which the reflow oven can be heated with the assembly in it, may be for example 200 degrees Celcius. By heating the assembly shown in Fig. 3H in the reflow oven, the second solder material 44 is soldered to the first solder material 34. The result is shown in Fig. 31, showing columns of solder material connecting pads 14 and 24, 15 and 25, and 16 and 26, respectively. It is remarked that, in view of restricting the use of lead in electronics, instead of using said lead containing materials for the first solder material 34 and for the second solder material 44, also suitable lead-free substances can be used.

It is furthermore remarked that the passageways through the second mask 40 have smaller length than those through the first mask 30, as can be seen by comparing the height of mask 40 shown in Fig. 3F with the height of mask 30 shown in Fig. 3B. A reason for this difference is, that the second solder material 44 substantially serves for soldering the first solder material 34 to the pads of the second component 20 and does not have the function to substantially contribute to the interconnection length between the first and second component, which is a function of the first solder material 34.

In Fig. 31 the solder materials 34 and 44, after being soldered together, are denoted in general by reference numeral 50. More in particular, the solder material 50 forming the connection between the first and second signal conductor ends 14 and 24 is denoted by reference numeral 54, and the solder material 50 forming the connection between the first and second signal shield ends 15 and 25 is denoted by reference numeral 55.

It is not strictly necessary for the described method that the connection of the second signal conductor end 24 to the signal conductor solder material 35 and the connection of the second signal shield end 25 to the signal shield solder material 36 are solder connections. Other connection methods are possible as well, such as methods using a hold-down mechanism with springs or the like. Reference is now made to Figs. 5A-5F, which schematically show, in a cross-sectional view similar to that of Fig. 4B, some other examples of the first solder material, after being soldered in a method according to the invention. Figs. 5A-5C show a few examples, wherein the signal shield solder materials 61, 63 and 65, respectively, have elongate parts which are not fully tangential with respect to a reference point at the signal conductors 60, 62 and 64, respectively, but which do have at least such tangential components. Figs. 5D and 5E show fully tangential signal shields 67 and 69, respectively. The signal shield 67 of Fig. 5D forms a ring having only one interruption. The signal shield 69 of Fig. 5E forms an uninterrupted ring. Fig. 5F shows an example, wherein the signal conductor solder material comprises two interconnected disk shapes 80 and 82, shielded by more or less elliptically shaped signal shield solder material 83. Such and similar configurations can be applied for example for making offset interconnections between wave guide ends of different components. Instead of elliptical shapes for the signal shield solder material 83, other noncircular shapes are possible as well, for example rectangular shapes.

Fig. 6 schematically shows a perspective view of an example of a solder mask 70 that can be used in a method according to the invention to form an uninterrupted shielding ring such as the ring 69 of Fig. 5E. The solder mask 70 comprises, through it, a cilindrical passageway 72 similar to the passageway 32 of the first solder mask 30 shown in Fig. 2A, as well as a ring shaped passageway 73 for receiving solder material meant for the shielding portion of the soldered interconnection means. The ring shaped passageway 73 separates a disk shaped portion 74 of the mask 70 from another flat portion 75 of the mask 70. In order to interconnect the separate portions 74 and 75, the mask 70 may comprise suitable bridging parts, such as tiny pins 76 extending within the passageway 73 and/or bridging parts 77 not lying within the passageway 73. The pins 76 have the advantage that they do not form an obstacle when removing, by a beam or another device, excess solder material inserted into the passageways 72 and 73. The bridging parts 77 have the advantage that they do not occupy any space in the passageway 73, which space preferably is to be allocated to solder material.

The above described methods according to the invention can be applied such that different heights of soldered solder materials are obtained for realizing different interconnection lengths between components.

For example, heights similar to known heights of balls of known Ball Grid Arrays could be used, which heights typically are 35 mils. Therefore, methods according to the invention can be integrated in the Ball Grid Array method (BGA). For example the pads 16 or 26 shown in Figs. 3A-3I may serve for attachment of BGA solder balls. However, for methods according to the invention, it is not necessary to form connections to the pads 16 or 26, or to even apply such pads 16 or 26.

Also, larger heights of soldered solder material are possible, for example similar to known heights of columns applied in known Column Grid Array methods (CGA). Such heights can for example be 50 mils or 87 mils. Due to these larger heights the columns of the CGA provide a higher degree of reliability compared to the balls of the BGA. The longer interconnection lengths between components achieved by the CGA give higher yield and better electrical performance than BGA, due to better mechanical stress relief.

The method according to the invention is particularly advantageous when applied in such CGA-like manner. This is because longer interconnection lengths increase the risk of signal disturbance, especially for higher frequencies, and therefore increase the need for a shielded waveguide interconnection that reduces the risk of signal disturbance.

Having described the invention, however, many modifications thereto will become apparent to those skilled within the art without deviation from the invention as defined by the scope of the appended claims. In particular the invention is not restricted to applications wherein a single signal shield configuration shields only one signal line. Applications, wherein a single signal shield configuration shields two or more separate signal lines are possible as well.

Claims

1. A shielded waveguide interconnection soldering method, comprising:

- providing a first component (10) comprising a first end surface (11) provided with at least one first shielded waveguide end (12) which comprises a first signal conductor end (14) and a first signal shield end (15); - providing a first solder material (34); and

- soldering the first solder material (34) to the at least one first shielded waveguide end (12) with the aid of a first solder mask (30), wherein, after soldering, the first solder material (34) comprises:

- signal conductor solder material (35) soldered to the first signal conductor end (14), and,

- signal shield solder material (36) soldered to the first signal shield end (15); characterized by

- applying at least part of the first solder material (34) in passageways (32, 33) through the first solder mask (30), which passageways are shaped such that, after soldering, the signal shield solder material (36) comprises, in a plane (M) substantially parallel to the first end surface (11), at least one elongated part (P) of which the longitudinal direction (L) has at least a component which is tangential with respect to a reference point (C) at the signal conductor solder material (35).

2. A method according to claim 1, further comprising:

- providing a second component (20) comprising a second end surface (21) provided with at least one second shielded waveguide end (22) which comprises a second signal conductor end (24) and a second signal shield end (25);

- connecting the second signal conductor end (24) to the signal conductor solder material (35) soldered to the first signal conductor end (14) and connecting the second signal shield end (25) to the signal shield solder material (36) soldered to the first signal shield end (15).

3. A method according to claim 2, wherein the connecting of the second signal conductor end (24) to the signal conductor solder material (35) and of the second signal shield end (25) to the signal shield solder material (36) comprises soldering by means of a second solder material (44).

4. A method according to claim 3, wherein at least part of the second solder material (44) is applied in passageways through a second solder mask

(40).

5. A method according to claim 3 or 4, wherein the second solder material (44) is chosen to have a lower eutectic melting point than the first solder material (34).

6. A method according to any of the preceding claims, wherein the method is integrated in a Ball Grid Array method.

7. A method according to any of the claims 1-5, wherein the method is integrated in a Column Grid Array method.

8. A first component (10) comprising a first end surface (11) provided with at least one first shielded waveguide end (12) which comprises a first signal conductor end (14) and a first signal shield end (15), wherein signal conductor solder material (35) is soldered to the first signal conductor end (14), and wherein signal shield solder material (36) is soldered to the first signal shield end (15), characterized in that the signal shield solder material (36) comprises, in a plane (M) substantially parallel to the first end surface (11), at least one elongated part (P) of which the longitudinal direction (L) has at least a component which is tangential with respect to a reference point (C) at the signal conductor solder material (35).

9. An assembly of a first component (10) according to claim 8 and a second component comprising a second end surface (21) provided with at least one second shielded waveguide end (22) which comprises a second signal conductor end (24) and a second signal shield end (25), wherein the second signal conductor end (24) is connected to the signal conductor solder material (35) soldered to the first signal conductor end (14), and wherein the second signal shield end (25) is connected to the signal shield solder material (36) soldered to the first signal shield end (15).

10. A solder mask for use in a method according to any one of the claims 1-7.

11. A solder mask according to claim 10, comprising at least one bridging part (76, 77) for bridging at least one passageway (73) extending through the solder mask (70).

12. A solder mask according to claim 11, wherein the at least one bridging part comprises at least one pin (76) extending within the at least one passageway (73).