Christopher Associates, US and Koki Solder, Japan have cooperated to study the increasing rate of head-in-pillow defects occurring in SMT soldering of BGA/CSP component soldering. Results have been published in a leading industry journal and will be discussed in a webinar in February.

Head-in-Pillow is a defect that occurs when a solder BGA/CSP solder ball sits on top of solder paste but their merger is interrupted during the reflow process, leaving the ball sitting inside a hollow solder mound.

It is already known that fluidity and heat resistance of the flux are important factors. If the flux does not sufficiently protect the solder particles or flow correctly during heating, wetting can be affected. Recent advances in paste technology have helped to reduce the occurrence of the defect.

This study found that in fact there are many potential causes of the effect, including board and component warpage, ball coplanarity and oxidation, paste volume and type as well as component placement and reflow profile used.

The report calls for development of standards on component and board warpage. The introduction on new halide-free fluxes may also require consideration.

The report of the work is published in two parts in the November 2009 and January 2010 issues of EngineerIT.

The SMTA-sponsored webinar will take place on February 4th 2010 - see reference link below.