Dimpled ball grid array qualification testing for space flight applications

With smaller and smaller Printed Wiring Board (PWB) form factors, such as CompactPCI^(R), the need for smaller packages with high I/Os has grown significantly. A Jet Propulsion Laboratory/NASA technology and system development program that services various spacecraft missions uses a 3U CompactPC^(R) form factor. The System Input/Output board requires a large amount of I/Os and has limited area, so conventional packages, such as quad flat packs (QFP) will not fit. Thus, the use of Ball Grid Arrays (BGAs) with much smaller package dimensions than leaded packages were needed to meet area requirements and were evaluated for space flight applications. Since this type of package has not been used in past space flight environments, it was necessary to determine the robustness and reliability of the solder joints. The D-BGAs were qualified by developing assembly, inspection and rework techniques as well as environmental tests. The test article was a printed wiring assembly (PWA) consisting of four daisy chained D-BGA packages. Visual inspection of the outer solder joints and real time X-ray were used to verify solder quality prior to testing. The test article was electrically monitored for shorts and opens at or above 1 μs during all environmental tests. Three environmental tests were conducted: random vibration at 0.2 g²/Hz, pyre shock at 2000 g for 50 ms, and thermal cycling from -55°C to 100°C for 200 cycles. After testing, Scanning Electron Microscope (SEM) analysis was performed on various DBGA cross sections to determine the quality of the package-to-board interface. The 472 D-BGA solder attachments passed the above environmental tests meeting the minimum requirements for use on space flight electronics