Design For Manufacturability Of PTH Solder Fill In Thick Board With OSP Finish
Authors: Shining Chang, Rocky Wang, Yu Xiang, and Paul Wang, Ph.D. Company: Mitac Computer Shunde Ltd. Date Published: 10/16/2011
Abstract: PTH often suffers poor hole fillet in wave soldering on OSP PCB. When PCB thickness reaches 2.7mm in server products and when the process is of lead-free, this issue has become more and more prominent. This paper studies how to achieve a good hole fillet by a good design of PTH hole. Two main factors are discussed here--- GND layer and Gap between the hole and the component pin. With minimum GND layers under electrical requirement and gap ratio of 15~20% (gap between PTH wall and PTH component pin is of (15 ~ 20%) *2.70mm, i.e. 0.40 ~ 0.54mm), a good hole fillet can be guaranteed. Further study also shows that such process parameters as flux volume and dipping time can be optimized to enhance wave solder capability and PCBA reliability when GND layer is reduced and hole diameter is enlarged. Further study also shows that flux type ought to be of high activity in dealing with 2.7-mm-thick PCB with surface finish of Enthone HT OSP type.