Reworking Of Pin Through Hole Components Using ‘Hot Air’- Paste In Hole Process
Authors: Guhan Subbarayan, Leo Anderson, and Rahul Raut Company: Cisco Systems, Inc., Flextronics International, and Cookson Electronics Date Published: 10/16/2011
Abstract: Pin Through Hole (PTH) components are traditionally reworked using a ‘Mini-pot’ solder fountain equipment. However, with the transition to lead-free electronics due to RoHS legislation, reworking using the ‘Mini pot’ equipment presents several challenges. The first challenge - achieving adequate holefill becomes more difficult and requires longer contact times, especially on Printed Circuit Boards (PCBs) with multiple layers of ground and power planes. The second challenge - combination of longer contact times and lead-free SAC305 solder alloy contribute to the issue of copper dissolution at the knee of the PTH barrel, leading to infant products failures. An alternative novel technique to rework PTH components is developed and studied in this paper. This technique is ‘Paste in Hole’ (PiH) rework using a ‘Hot air’ BGA rework equipment. A limitation of this method is achieving good holefill for thick PCBs ( > 93 mils). In this case, for the purpose of obtaining adequate holefill, solder preforms in size of chip components would be added to the solder paste to provide supplemental solder volume. The important requirements for this technique are that the PTH components should be able to withstand the SMT reflow temperature and have adequate standoff height for placing solder preforms underneath the component body. In this study, three types of types of PTH components (Power brick, fine pitch header and RJ45 connector) were reworked 1x and 2x times using the ‘Mini pot’ and ‘Hot Air’ rework methods. After both rework processes, the PTH components were cross-sectioned and examined for copper dissolution at knee of the barrel. The copper dissolution and holefill results were compared and discussed. The design, process and equipment considerations for the ‘Hot Air’ rework process are discussed and presented with great detail in this paper.