Extra thin profile land grid array package solder joint reliability assessment

Handheld and portable consumer electronics devices are getting lighter and smaller these days. As a major consumer electronics storage device, hard drive has gained its acceptance rapidly as one of the choices for higher reliable, lower price and faster accessing consumer electronics applications. Design of printed circuit board assembly for hard drives is hence moving towards higher performance and smaller form factor, which drives the need for smaller and thinner packaging solutions to support low vertical profiles and satisfy the cost sensitive demands. In the present studies, the extra thin profile land grid array packages were utilized for the printed circuit board assembly in order to meet the height restriction of the hard drive for consumer electronics applications. According to the hard drive reliability requirements, the assembled boards were tested under the temperature cycling, thermal shock, bias temperature humidity, high temperature on load, and mechanical flex and bend. Finite element analyses were also conducted to simulate the solder joint mechanical responses under the reliability test conditions. Since the effects of the laminate substrate and thin small die, the simulated solder joint stresses were relatively lower compared with some previous packages. It was then expected that the package solder joints would be more robust and survive longer under the thermal loading. This conclusion was in agreement with actual reliability test results in which all the boards met the reliability requirements. For consumer electronics applications, drop test is another critical test condition to evaluate solder joint reliability performance. Because of the excessive flexing of the current printed circuit board design, the relative motion between the board and the mounted packages was more significant during the drop test which might result in severe solder joint failures. It was found from the drop test that the critical solder joint occurred at the outermost corner for the large package, and fails occurred between the solder and PCB pad interfaces. With the underfill protection, the solder joint impact life could be improved dramatically.