关键词: 双层基板, 塑封器件, 扫描声学显微镜, 分层假象

Abstract: When scanning acoustic microscope is used to inspect plastic encapsulated devices on double-layer substrates, the understanding of device structure and acoustic scanning equipment imaging is insufficient, which is easy to lead to misjudgement. Through chemical unsealing and physical anatomy analysis of two kinds of FPGA devices with double-layer substrate structure produced by ACTEL Company. At the same time, comprehensive analysis and verification are carried out from many aspects, such as the characteristics of device detection waveform, the characteristics of acoustic scanning image, and the comparative verification of similar devices.It is pointed out that when the threshold contains two or more main wave signals, the package structure of the device should be paid attention to. After the device structure is fully understood, the interface wave corresponding to the focus interface is selected through the threshold setting, and then the correct result can be obtained by acoustic scanning.

Key words: double-layer substrates, plastic encapsulated devices, scanning acoustic microscopy, stratified illusion