Case I: Plating Issues- The EMPF recently received an email from a customer looking for help with plating issues. The customer assembles hybrid microelectronic components used solely in electronic controls. However, some of these hybrid packages have gone unused for a long period of time, and have become oxidized. The customer wanted to know if these packages can be saved by stripping and replating the surface.

Additional information was given to the EMPF on the packaging materials, structures, original plating processes, and final surface finishes. After reviewing the information, the EMPF’s expert team made some suggestions and recommendations to the customer. The first observation was to confirm that the top coating material is strippable. The action that the customer needed to take was to determine the oxidation layer thickness by Augar analysis. If the base material was not affected by the surface oxidation, a stripping process could be established by using suitable chemical solutions. Secondly, the customer was advised to consult the original plating vendor for possible sources for stripping the top layer coating without damaging the base material. The EMPF also contacted several plating companies and made recommendations on the solutions that could be used for stripping the top coating.

Case II: Process ceramic column grid array packages
A customer was under a contract to assemble hardware for an aerospace application that involves the use of BGAs (Ball Grid Arrays), uBGAs (micro Ball Grid Arrays), other gull wing devices, and ceramic column grid array packages. When the customer was assembling the ceramic column grid array packages on the boards, some concerns were raised. Specifically, the recommended volume of solder paste to be used was 20% greater than the actual volume that should have been applied. When the recommended volume on the customer designed pads was applied, the excess amount of solder pushed the column off of the pad (Figure 4-1). When the solder paste amount was reduced to two thirds of the recommended amount, the solder joints showed insufficient coverage (Figure 4-2).

The EMPF agreed with the customer that the insufficient amount of solder paste would be a concern for the long term reliability of their solder joints. Their proposed solution was to file down the bullet shaped points of the columns to prevent the part from moving so much. The EMPF recommended against this for two reasons. First, the bullet shape of the column end is specifically intended to aid in self-centering during re-flow. Secondly, external stress might be introduced into the solder joints by using this method, and could affect its long term reliability. The EMPF’s recommendation was to reduce the solder paste amount by 20%. That proposed solution should reduce or eliminate the solder push-out, while still allowing enough solder volume to provide a properly wetted joint.

The volume reduction also compensated for coplanarity variance, a state where one or more parts of a component rests higher or lower than another. The even deposition of solder paste on the stencil would allow the component planes to line up, thus producing an even component seating.

If you have any questions about this article or any of the topics, please contact the EMPF helpline at (610) 362-1320. A manufacturing expert will be able to offer technical insight and appropriate advice regarding your concerns.