Discriminating defects method for plastic encapsulated microcircuits by using scanning acoustic microscope

摘要

Scanning acoustic microscope (SAM) is widely applied to the screening and detection of plastic encapsulated microcircuits (PEMs) because of its high sensitivity and nondestructive characteristic. However, existing methods uses SAM to focus on six interfaces one by one, which is time consuming and inefficient. In this paper, based on the analysis on defects of PEMs and discussion about existing SAM standard, the scanning method for detecting defects in PEMs was proposed. In the proposed method, A-scan and C-scan were used to detect voids, cracks and delamination inside PEMs. The process was divided into two parts including package inspection and important interfaces inspection. It uses SAM to only focus on the lead frame to observe three top view interfaces and two back view interfaces. Compared with existing methods which use SAM to focus on six interfaces, the proposed method focuses on only two interfaces to observe them, which can save time and improve detection efficiency using SAM. 50 devices of plastic encapsulated flash were used to store at 125, 150, 175 centigrade for 600, 900, 1200 hours respectively which can which can stimulate internal defects of flash. After 1200 hours' high temperature storage, 27 devices have delamination, 2 devices have cracks and one device has voids. The defects which are stimulated by high temperature storage are detected and analyzed by the method mentioned in this paper to verify the applicability and validity of it.