CN1386609A - Electronic package solder ball structure - Google Patents

Abstract

The electronic package solder ball structure is characterized by that said solder ball is made up by using metal whose melting temp. is progressively reduced from interior to exterior, its interior is a metal ball core whose conductivity is good and melting point is higher than that of its exterior, and its exterior is covered with low-temp. metal. The invention has the characteristics of good multiple-time processability, good strength after welding, high compatibility with a substrate welding material, less deformation, convenience for testing, low resistance, low cost and the like.

Description

Electronic package solder ball structure

The invention relates to electronic packaging, in particular to an electronic packaging solder ball structure.

The main function of the solder ball is to supply a certain volume of solder material in a controllable manner when welding small components.

The temperature range of soldering IC (integrated circuit) or electronic substrate is carried out in the most suitable range of substrate packaging temperature of 210-230°C. During actual operation, due to differences in air flow, substrate 3 heating method, actual density, parts, etc., the difference in heat absorption and heat dissipation affects the uniformity of temperature. During soldering, some parts may be lower than the set temperature by 10°C or 20°C, etc. At this time, the relatively low temperature part will have poor solder condensation and poor tin intake. If the temperature is increased to the point where the relatively low temperature part can fully absorb tin, the surface of the solder 1 will collapse 2 in the relatively high temperature part (as shown in Figure 1).

If the soldering of more than two layers is implemented, it will easily fail, and the high-temperature part will completely separate the second-layer substrate 5 due to temperature unevenness and high-temperature part.

In terms of multiple processability, in response to the development of current requirements, multi-layer packaging will become inevitable. For multi-layer packaging, due to the difficulty in construction, it is necessary to adopt multi-layer and multiple welding to meet the requirements. In this case, the solder joints must be able to withstand repeated heating without deformation. That is to say, when the previously welded solder joints are repeatedly heated to the melting point during repeated heating, they cannot collapse or crack due to the re-melting of the solder joints...etc. Failed to re-solder.

The main purpose of the present invention is to eliminate the above disadvantages and provide a solder ball structure for electronic packaging. The melting temperature of the solder ball decreases gradually from the inside to the outside, and has good multiple processability, good post-soldering strength, and the same solder material as the substrate. High capacitance, less deformation, easy to test, low resistance, low cost and so on.

The object of the present invention is achieved like this: an electronic packaging solder ball structure is characterized in that: the solder ball is made of metal whose melting temperature gradually decreases from the inside to the outside;

The solder ball has no obvious delamination from the inside to the outside;

The solder ball is made from the inside to the outside of a metal core with a higher melting temperature than the outer layer and the outer layer is coated with a low-temperature metal with more than one component or two components;

The center is made of platinum, gold, silver, tin, tin silver, tin silver copper, tin copper or silver copper low resistance metal;

The outer cladding is made of tin, antimony, lead, bismuth, indium metal or alloys thereof;

The outermost layer of the solder ball is also coated with an anti-oxidation layer;

The center of the ball is also a multi-layer metal cladding structure.

The advantages of the present invention are:

1. When the solder ball of the present invention is used for the packaging and welding of IC or substrate, the high melting point of the solder ball is not melted and has a contour line, and the outer layer of liquid-melted substrate is good for tin, and has good multiple processability and good post-soldering Good strength, high compatibility with substrate welding materials, less deformation, easy testing, low resistance, low cost and other characteristics.

2. The center of the solder ball of the present invention is made of cheap tin or tin-copper alloy, and the more expensive low-temperature metal is only used as the outer low-temperature layer coating, so the amount of use is significantly reduced and the cost can be reduced.

3. The solder ball of the present invention has a high melting point spherical center, so the solder ball center of the solder joint is not melted and can maintain a certain solder joint height, so that each solder joint has the same height, and the test operation is easier and more reliable.

About technology, means and effect thereof that the present invention adopts, give a preferred embodiment hereby and describe in detail in conjunction with accompanying drawing in the following:

Figure 1 is a partially enlarged planar cross-sectional view of a conventional solder joint.

Fig. 2 is a partial enlarged plane sectional view of conventional welding with more than two layers.

Fig. 3 is a partially enlarged schematic plan view of the solder ball structure of the electronic package of the present invention before soldering.

FIG. 4 is a schematic plan view of contour lines after soldering of the electronic packaging solder ball structure of the present invention.

Fig. 5 is a partial enlarged plan view of the solder ball structure of the electronic package of the present invention after double-layer soldering.

Fig. 6 is a partially enlarged schematic plan view of the double-layer solder ball structure of the electronic package before soldering according to the present invention.

FIG. 7 is a schematic plan view of the post-soldering test of the electronic packaging solder ball structure of the present invention.

Fig. 8 is a partially enlarged schematic plan view showing the comparison between the present invention and the single-layer welding of the practitioner.

Fig. 9 is a partially enlarged plan view showing the comparison between the present invention and the double-layer welding of the experienced user.

In the picture:

1-Solder 2-Collapse

3-substrate

5-Second layer substrate 6-Sink phenomenon

7-Solder Ball 10-Electronic Substrate

11-The first layer of substrate

20-solder ball 21-ball center

22-Low temperature metal 30-Contour

40-solder point 41-test contact point

An electronic packaging solder ball structure according to the present invention is shown in FIG. 3 . An electronic package solder ball structure is mainly an invention for solder balls 20 packaged and soldered to an IC or an electronic substrate 10 . The main function of the solder ball 20 is to controllably supply a certain volume of solder when soldering small components. The invention is made of materials that are not layered from the inside to the outside, and the melting temperature is gradually lowered from the inside to the outside. The melting point is gradually lowered from the inside to the outside, and the central part can only melt when it exceeds 230°C. The closer to the epidermis, the lower the melting point, and the outermost layer can be lower than 180°C. There is no hierarchical method, and the metal is stacked with two or more low-temperature metals by ion reduction method or other related methods. Alternatively, the core 21 is made of a metal with a melting temperature higher than that of the outer layer, and the outer layer is a solder ball 20 made of a metal 22 with a low melting point. The outermost layer of the solder ball is also coated with an anti-oxidation layer. The following compares the present invention with the conventional soldering conditions as follows: the most suitable substrate 10 packaging temperature range is 210-230°C for soldering. During actual operation, due to differences in air flow, substrate heating method, actual density, parts, etc., the difference in heat absorption and heat dissipation will affect the uniformity of temperature. During welding, some parts may be lower than the set temperature by 10°C or 20°C. For those who are used to it, at this time, the relatively low temperature part will have solder condensation and bad tin eating. If the temperature is raised to the point where the relatively low temperature part can fully absorb tin, the relatively high temperature part will cause the solder surface to collapse. Welding on more than two layers will easily fail. The present invention can avoid above two kinds of temperature problems, because soldering point has a contour line 30 (referring to Fig. 4), so when welding (referring to Fig. 5) above the second layer, can guarantee the upper and lower two sides of each soldering point Both the side of the first layer of substrate 11 and the side of the second layer of substrate 12 can eat tin, and there will be no solder joint collapse. The high-melting-point ball center 21 is not melted, and the outer low-temperature layer has fully become liquid-melted, so the outer layer has good fluidity, which can ensure its ability to eat tin.

In terms of multiple processability, multi-layer packaging will become inevitable in response to the development of current requirements. For multi-layer packaging, due to the difficulty in construction, it is necessary to adopt multiple layers of welding to meet the requirements. In this case, the solder joints must be able to withstand repeated repetitions without deformation. Flowing and collapsing, cracking, etc. cause failure. Because the present invention has a high-melting point ball center 21 (referring to shown in Figure 5), it can endure repeated heating without deformation, because when heating to the welding temperature again, although the outer layer is melted again, the ball center 21 is still not melted. A certain supporting strength can be maintained without deformation and collapse, so the solder ball 20 of the present invention can make the multi-layer packaging operation reliable and easy to implement.

As far as solder strength is concerned, the soldering base metal on the substrate is different, and even the use of lead-containing base metals and soldering materials is prohibited in countries around the world due to environmental protection issues. The main component of lead-free soldering materials is still tin, combined with other low Melting point metals such as bismuth, indium, etc. . . . However, metals such as bismuth and indium have poor brittle strength. The high melting point spherical center 21 of the present invention does not contain brittle metals. The low melting point metal 22 (shown in FIG. 6 ) is only used in the outer cladding. The welded finished product has the strength support provided by the spherical center 21. Affected by the brittleness of low-temperature welding consumables, it can be effectively reduced.

As far as the compatibility between the material of the substrate 10 and the components of the welding material is concerned, there may be many kinds of materials for the different welding points of the substrate on the circuit connection, and the welding material is designed according to the compatibility of the substrate material. tin capacity. But the welded product may not have good strength. If you consider the strength of solder joints, the ability to eat tin and stick to tin must be compromised. In the present invention, there is a high-melting-point ball center 21 inside, and the ball center can be made of stronger material, so that the welded product maintains strength. The low melting point part of the outer layer can be manufactured selectively according to the tin-eating ability of the substrate material, that is, the compatibility requirements between the base material and the welding material.

Base material: refers to the material used to provide circuit connections and solder points on the substrate. Solder material: refers to the solder ball (Solder Joint).

In terms of solidification shrinkage and stress, package solder joints are heated and melted on the substrate. When the solder joints are molten, due to the influence of other factors such as the surface material of the substrate, the ability to absorb tin is prone to vary. Therefore, the shape of each solder joint will vary. There is a difference. When solidified, the difference in solidification shrinkage will be affected by the difference in shape. If more than two layers of welding are made, the difference in solidification shrinkage will produce extreme stress, which is the main cause of solder joint cracks. Because the present invention has a high-melting-point sphere center 21 exceeding the welding temperature, there is less deformation and less shrinkage during liquid melting, which can reduce deformation and avoid cracking of solder joints.

As far as testing is concerned, the present invention is convenient for testing, because there is a high-melting-point sphere center 21 exceeding the welding temperature, and the outer layer and the substrate 10 contact the outer layer melting solution during welding, and the height will be reduced due to the surface strength, that is, the outer layer of the sphere is deformed. The inner core 21 remains substantially unchanged since the melting point has not been reached. Therefore, the welding spot 40 can be kept at a certain height when the welding is completed. There may be hundreds of solder joints 40 on the same substrate 10 . The high melting point spherical center 21 can maintain a certain height of the solder joint 40, so that each solder joint and test contact point 41 have the same height. So the test operation will be relatively easy and reliable (see Figure 7).

In terms of resistance, solder joints or solder joints 40 are usually used as circuit connections on the substrate, and lead, bismuth, indium, etc. contained in solder materials of solder joints 40 are poor conductors of electricity. It is very easy to form resistance on the soldering point, making the temperature of each soldering point inconsistent, causing thermal differences among various parts, reducing stress life, and malfunctioning. The present invention can make the low-melting-point metal 22 of poor conductor only be used on the surface layer of the welding material and control its amount. The high melting point spherical core 21 is not melted during the welding work. Therefore, platinum, gold, silver, tin, tin-silver, tin-silver-copper, tin-copper, silver-copper, etc. can be used as the composition of the ball center 21 to meet the low-resistance requirement of the solder joint 40 .

In terms of cost, packaging solder is generally an alloy of 63% tin and 37% lead. Lead-free tin solder is the main material plus other low-melting point materials such as bismuth (BI) or indium (IN) to lower the melting point. Because low-temperature metals other than tin, such as bismuth and indium, are expensive. The center 21 of the present invention is relatively cheap tin or tin-copper alloy. And other relatively expensive low-melting point metals 22 are only used as the cladding of the surface layer, so the usage amount is obviously much less, and the cost can be reduced.

Referring to FIG. 8 , after the conventional solder ball 7 is placed on the substrate 3 (as shown in a) and soldered, it may become more normal as shown in FIG. b or melted on the substrate 3 as shown in FIG. c;

After the solder ball 20 of the present invention is placed on the substrate 10 (as shown in d) and soldered, the surface liquid is melted and the center 21 of the ball is not melted (as shown in e and f).

Referring to Figure 9, the conventional solder ball 7 is placed between the first and second layer substrates 4 and 5 (as shown in a), after soldering, it may become the normal state of the figure b or the cracked, deformed state of the figure c or The collapse of figure d forms an open circuit state;

The solder ball 20 of the present invention is placed between the first and second-layer substrates 11 and 12 (as shown in e), after soldering, the high-melting point ball center 21 is not melted and forms a support, so that the substrate and the surface layer are melted to eat tin The condition is at its best (as shown in f, g, h).

In summary, it can be known that the present invention has excellent progressive practicability among similar products.

The above-mentioned embodiments are only used to illustrate the present invention. It is hereby declared that all variations, modifications and applications made according to the present invention shall belong to the protection scope of the present invention.

Claims (7)

1. An electronic packaging solder ball structure, characterized in that: the solder ball is made of metal whose melting temperature gradually decreases from the inside to the outside. 2. The electronic package solder ball structure according to claim 1, wherein the solder ball has no obvious layering from inside to outside. 3. The electronic packaging solder ball structure according to claim 1, characterized in that the solder ball is a metal ball core with a higher melting temperature than the outer layer from the inside to the outside and the outer layer is coated with more than one single component or Made of low-temperature metals with two or more components. 4. The electronic packaging solder ball structure according to claim 3, wherein the ball center is made of platinum, gold, silver, tin, tin-silver, tin-silver-copper, tin-copper or silver-copper low-resistance metal. 5. The electronic package solder ball structure according to claim 3, wherein the outer coating layer is made of tin, antimony, lead, bismuth, indium or alloys thereof. 6 . The electronic package solder ball structure according to claim 1 , wherein the outermost layer of the solder ball is coated with an anti-oxidation layer. 7. The electronic packaging solder ball structure according to claim 1, wherein the ball center is also a multi-layer metal cladding structure.

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