Authored By:
Gabe Cherian
Cherian LLC
Sun Valley, Idaho USA
Summary
Most electronic assemblies comprise a number of chips, packages and similar components that are attached to Printed Circuit Boards (PCBs) or similar substrates, usually using solder joints. Also most frequently, the components and the substrates are made of materials that have different Thermal Coefficients of Expansion. If such assemblies get exposed to harsh environments, such as severe thermal cycling, or to frequent power cycling, then they run the risk of having their solder joints stressed, and in some cases, the stresses can reach a level where some joints would fail. This is especially true, when the components are relatively large in size, like half an inch square or larger, and when the temperature variations are fairly large.
It is well known that if the solder joints are tall, like columns, stretching between the components and the substrate, like the Solder Column(s) with Copper Tape, then the induced stresses in the joints are reduced and the assemblies can more readily survive such harsh conditions. This paper discloses some additional novel features, which enhance the performance of such column-like joints, which make such joints even better than traditional columns, and enhance the reliability and extend the operating life of such electronic assemblies.
The columns in this case have an elongated cross section, and are oriented in a way that presents the lowest resistance to flexing in the direction of the thermal deformation of the assembled components. The concepts have been applied also to leaded components, by orienting their leads. The paper describes a number of such design concepts and embodiments. Some of them are already patented, while others are still patent pending.
Conclusions
I have described several concepts for creating solder joints between BGAs and Substrates, or similar electronic assemblies, which could be used to improve the operating life and reliability of such assemblies. Most of these new concepts are just that, just concepts. They need to be prototyped and tested, and most probably, they would need to be tweaked or further developed, before they would become viable products or methods, which can be accepted by the industry.
As this stage, the best that can happen is that some interested parties would come forward and volunteer to provide the effort and facilities, to do the required development work. I am more that willing and ready to work with such parties on such development work.
Initially Published in the IPC Proceedings
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