Study on Manufacturing Process of Semi-flex Printed Circuit Board Using Buried Material

In this paper, the semi-flex Printed Circuit Board (PCB) was manufactured by using buried material to prevent resin of high-flow prepreg from flowing into the flexible area in lamination process. Windows in which the buried materials were imbedded were shaped in advance in prepreg and cores. The circuit in flexible area was protected by polyimide (PI) cove layer. The preventing capability of resin for the three different buried materials including epoxy resin base material, silicon sheet and Teflon (PTFE) were studied by microsection manufacture and Optical Critical Dimension, and the results showed that the silicon sheet was the most appropriate one. Manufacturing processes such as the heating rate in lamination process, sizes of silicon sheet and windows of prepreg were studied by the orthogonal tests and the optimal manufacturing parameters were analyzed and achieved by Minitab Software. Several demonstration tests were conducted under optimal manufacturing condition and the results including resin length and flexural ability were acceptable. The reliability of semi-flex PCB was evaluated by solder float test, thermal shock test and salt spray test. The results showed that the flexible area had substantially no defects such as bubbles, separation and flaws occurred and delamination had not occurred in the rigid-flex joint of the products, and the resistance value change was 5.37% in thermal shock test. The reliability of semi-flex PCB was acceptable.