Publication: Finite element modeling of warpage molded printed circuit board in a reflow process
Date
2022-05-01
Authors
Sek, Chun Hei
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Abstract
A printed circuit board (PCB) consists of multi-layer materials that allow electrical current flow. Each material layer has its own specific coefficient thermal expansion (CTE), such as
Young’s modulus, Poisson’s ratio, etc. A conventional PCB board consists of polymer, silicon, copper, and dielectric. With each layers having different CTE values, this causes PCB to warp.In the semiconductor industry, PCB warpage has greatly impacted assembly process yield and solder joint reliability. The present study explores the warpage changes of molded PCB during the reflow process. Warpage behavior on molded PCB models has been investigated experimentally and numerically. Experimental set-up employs Shadow Moiré technique to measure real-time warpage measurement for a benchmark model with the size of 10 × 10 ×1 mm. Temperature profile with progressive heating from 25 ℃ to 300 ℃ with an interval of 50 ℃ is employed. Then, the sample undergoes a cooling process until it reaches the room temperature. Numerically, ANSYS FEA simulation was carried out to investigate the warpage on different sizes of PCB models. In addition, thermal stress induced by CTE mismatch is studied to understand its impact on PCB warpage. The results revealed that the experiment and the FEA simulation results are in a good agreement, in particularly at the peak temperature of 300 ℃, with less than 5 % deviation between both results. Moreover, the overall package warpage had also been influenced by package size in the reflow temperature. In addition, the results lead to the suggestion that the thermal stress exerted on the contact surface between different material types could lead to PCB warpages. The present research has established FEA that obtaining good warpage prediction model. The insights attained from this study would be beneficial for PCB design improvement, by optimizing materials and dimensions of PCB, in the attempt to minimize the warpage occurrence.