The Pros And Cons Of The Popcorn Failure

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Reliability is defined as the ability of a system or component to perform its required functions under stated conditions for a specified period of time. The operation of any electronic device generates heat and with the increasing device density of the IC chips the amount of heat flux generated by the integrated circuit chips has gone to a level of 100-200 W/(cm^2 ) [2]. Each time a device is powered up, the individual components heat up and cool down. This heating and cooling leads to thermal cycling of the electronic components which causes many problems, such as shear deformation, due to the mismatch in coefficients of thermal expansion (CTE) of each material. Figure 2.1 shows the varying CTEs for a typical PBGA package in this research.…show more content…
A disadvantage of plastic moulding compounds is that they are hydrophilic and absorb moisture when exposed to a humid environment [4]. This popcorn-like explosion happens when moisture that is trapped inside the moulding compound becomes heated and vaporized during the solder joint reflow process and the only way for it to escape is to expand the moulding compound until it cracks and the vapor is released. After investigated the moisture sensitivity in several surface mount packages that included SOJ, PLCC, TQFP, and PQFP packages. A researcher studied the moisture induced failures of Ball Grid Array packages such as PBGA and TBGA. They showed that baking the chips at 115°C for sixteen hours essentially removes most of the moisture content from the package, and reduces the possibility of the interfacial delamination and popcorn cracking of the package. By encountering this popcorn cracking, it is used to propose a new lead frame design for improved reliability of these…show more content…
In this study, structural and thermal reliability of ball grid array packages, mainly the shear stresses and strains of critical solder balls, have been investigated using accelerated life testing. Many studies and failure analyses have been showing that interconnect failures due to mismatches of CTE during thermal cycling is the most critical mode of failure in leaded and SMT packages such as BGAs [5]. Figure 2.3 shows a schematic of what happens to the solder joints during thermal cycling due to mismatches in CTEs. It shows that at a stress-free temperature, the two components, silicon and the PCB, are relaxed. Then, as the temperature increases, the PCB wants to expand at a higher rate since the PCB’s CTE is 14.5 ppm/°C and the CTE of the silicon is 2.54 ppm/°C. As the temperature drops, the PCB wants to contract much quicker than the silicon. Looking at the schematic, one can see that the solder joints are having to flex and deform due to the mismatch in CTE between the two materials. Over time, these shear stresses and strains cause the solder joints to become fatigued, then cracks begin to propagate, and the package will ultimately fail once a certain number of thermal cycles have been
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