Integrated nCTF pad design on PCB for BGA solder joint reliability enhancement

Abstract

In PCBA manufacturing industry, corner adhesive was commonly used on BGA(Ball Grid Arrays) to resolve the solder joint crack induced by mechanical stress either during shock and vibration reliability test or during board manufacturing processes(ICT test fixture, router, handling and etc) especially for mobile motherboard. However, this solution imposed high manufacturing cost which required additional glue processes with more process control, additional equipment setup for adhesive dispenser and curing oven as well as additional material cost for the adhesive. Besides that, the BGA with corner adhesive is difficult to be reworked especially for high-temperature curing adhesive. A new approach in PCB design for BGA called integrated nCTF(non critical to function) or dummy pad has been developed to replace the costly corner adhesive to address the problem of solder joint crack induced at post board level shock and vibration reliability test as well as time-0 solder joint crack induced by mechanical stress during board manufacturing. This paper will review the land pattern of the integrated nCTF pad design, stencil opening design, evaluation plan and the results of CTF(critical to function) solder joint crack percentage comparison between integrated nCTF pad and individual nCTF pad as well as to show the bulky solder joint formed on the integrated nCTF pads.