Cause of BGA Solder Joint Bridging

Mr. Zarrow has been involved with PCB assembly for more than thirty years. He is recognized for his expertise in troubleshooting SMT manufacturing and lead-free implementation. He has extensive hands-on experience with set-up and troubleshooting through-hole and SMT processes throughout the world.

Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

Mr. Bernard has been the X-ray Systems Product Manager at Dage for over 5 years and have been involved in all aspects of x-ray inspection and test for printed circuit board assembly applications. Prior to this, Dr. Bernard was working with radiation measurement instrumentation.

Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

An other possible cause of bridging on BGA components that your experts did not talk about concerns the PCB design. When you have vias in pads without filling, the organic medium of the solder paste is trapped in these small "bowls". Flux, solvents, couldn't desorb enough and this generates voids. If you have a picth between balls under 1mm, it could be generate bridging.

BGA solder joint bridging may also be because of excessive warpage of BGA device. It essentially occurs when there is some mismatch between the various components that make up a BGA Package (i.e. the substrate, molding compound and silicon chip). Too much warpage creates stress on solder balls and cause Bridging and opens. The warping can be very slight - in this case, the center of the BGA will bow upwards, and the corners down - but it's often enough to cause the corners to move closer to the circuit board surface, putting extra pressure on the corner solder joints to cause bridging.