Patent Application
20120298406
The present invention relates to solder joints in printed wiring board integrated circuit technology, and particularly printed wiring boards using gull wing connectors.
Microelectronic components are being continually miniaturized into area arrays. However, in these miniaturized area arrays, the reliability of solder joints is becoming increasingly significant. This is especially true with solder joints for gull wing connectors. Because of the cantilever structure of gull wing connectors, the solder joints are subject to increased structural stress.
Voids in the solder joint have been studied in the microelectronics art for their effect on solder junction reliability. Please refer to the article, “Effect of voids on the reliability of BSA/CPS solder joints”, Microelectronics Reliability, Vol. 43, 2003, pp. 2077-86.
I have found that intentionally created voids of controlled size can be used to increase junction reliability. I have further found that micro-vias, which are conventionally used for vertical connections in wire or circuit boards may be used for an entirely different purpose; the micro-vias may be used in the creation of solder joints to initiate the controlled formation of voids that, surprisingly, increase the reliability of the solder joints. Micro-vias are minute drilled horizontal holes in circuit boards that have a diameter of less than 6 mils, which are normally used to interconnect component contact.
In the present invention, the micro-vias are used beneath solder joints without any horizontal interconnectors for the sole purpose of creating voids. Accordingly, the present invention provides a method of forming a gull wing solder joint that comprises, first, forming a metallic mount pad on a printed wiring board (PWB). Then a central micro-via is formed in the mount pad. The micro-via is formed by any conventional method of forming micro-vias, such as microelectronic drilling mechanically or by laser. However, the drilled micro-vias are not conventionally vertically drilled through layers to provide interconnection routes. Herein, the drilled micro-vias form recesses in the mount pads that provide sites from which gases may expand during the thermal flowing of the solder to form the desirable voids in accordance with this invention.
At this point in the process, the solder paste is applied over the mount pad and associated micro-via, metallic gulf wing connector lead set on the solder paste, and the solder paste is thermally reflowed to thereby connect the connector lead to said pad to form a solder joint having a void co-extensive with said micro-via.
The present invention will be better understood and its numerous objects and advantages will become more apparent to those skilled in the art by reference to the following drawings, in conjunction with the accompanying specification, in which:
Now with reference to
Then,
At this point, the gull wing connector 14 is placed against solder paste 13, and appropriate heat is applied to thermally flow solder paste 13,
The resulting final structure is shown in
Now with reference to
Then,
At this point, the gull wing connector 14 is placed against solder paste 13, and appropriate heat is applied to thermally flow solder paste 13,
The resulting final structure is shown in
Although certain preferred embodiments have been shown and described, it will be understood that many changes and modifications may be made therein without departing from the scope and intent of the appended claims.
