Solder void criteria of BTC component investigation

There are no criteria for Bottom Terminal Component (BTC) solder void except 30% area for BGA solder joints in IPC-A-610F. It means supplier and customer should co-define the criteria for their own products. The solder void ratio control is related to many factors including PCB surface treatment, component soldering terminal condition, solder paste selection, footprint design, stencil aperture design, reflow profile, etc. In this paper, we focus on System in Package (SiP) modules including molding and metal lid types to investigate the impact of void inside BTC solder joint post reflow. The parts include Crystal and QFN that only have solder joint beneath component body. Firstly, to confirm the solder void ratio changes before and after reflow of pre-condition test, humidity absorbing then passing 3 times reflow. Secondly, keep monitoring the reliability test result after Thermal Cycling (TC), Unbiased Highly Accelerated Stress Test (UHAST) and Temperature Humidity Bias (THB). From the data collection known, solder void changed during reflow of pre-condition. Even if the solder void become larger, the solder joint reliability still not become worse and passed all the test items and cycles. It means the risk of BTC solder void won't cause reliability issue in our cases even the void reach 60%. According to this investigation, we don't need to scrape the samples with larger void before reliability test but follow up the test result. This way, we won't waste time and money for re-building a lot for reliability. Furthermore, since the solder joint void had been qualified by reliability test, we can set up a wider window for in-process quality control.