Plastic-encapsulated microcircuits PEMs

The decision to rework electronic devices or assemblies depends on the cost of reworking versus the value of the part. Consumer electronics, due to their low cost, are considered throwaways and seldom reworked. For some, such as plastic-encapsulated microcircuits (PEMs) that are produced in high volumes, rework is impractical because of the difficulty in removing the plastic encapsulant without destroying the components. However, for high-value assemblies, such as densely populated PWBs and MCMs, where the final value may be as high as 10,000 or more, the ability to rework is essential. In such cases, rework may be necessary to meet schedules when small numbers of assemblies are produced. 

Adhesives are also tailored to meet specific requirements of the packaging or assembly technology used (Table 5.9). Thus, the requirements for single-chip packaging in hermetically sealed ceramic packages such as CERDIPs will be somewhat different from those of plastic dual-in-line packages (PDIPs) and plastic-encapsulated microcircuits (PEMs). 

Physics of failure for plastic-encapsulated microcircuits (PEMs) 292... 

If package cracks are suspected, a dye penetrant test should be performed. In this test, a fluorescent dye is applied to the package surface and then wiped clean. Examination of the part under UV-light reveals residual dye in package cracks. This test is applicable both to hermetic parts and plastic-encapsulated microcircuits (PEMs). 

Scanning acoustic microscopy (SAM) is an ideal nondestructive method for revealing internal flaws within materials or between material interfaces. SAM is extensively used in detecting voids, delamination, and other separations that can occur in adhesive-attached parts, especially after thermal cycling. SAM is particularly useful in the analysis or evaluation of many types of electronic parts, including ceramic and plastic-encapsulated ICs, plastic-encapsulated microcircuits (PEMs), hybrid micro-circuits, CSPs, PBGAs, and printed-wiring boards. 

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