Journal of SMT Article
Lead-Free PTH Rework Process Challenges And Solutions For A Complex Server PCBA
Company: IBM Corporation and Celestica Inc.
Date Published: 7/29/2010 Volume: 23-3
A particular challenge in lead free processing of products in the server space is the assembly of the PTH (Pin Through Hole) components. The card thickness of these complex servers can exceed 130 mils with layer counts exceeding 20 layers. Additionally multiple layers of one and two ounce copper planes further complicate the wave process and rework of the PTH components.
Achieving adequate hole-fill during initial assembly and rework is considerably more difficult in complex servers, especially in cases of ground or power planes that are connected to multiple layers. Rework is further challenging as the elevated lead free processing temperatures drive longer solder contact times which contribute to copper dissolution of the PTH barrel due to the Pb-free metallurgy. With these additional challenges, traditional methods of PTH rework may not give acceptable results.
This paper presents design and process considerations and a new methodology for PTH rework where traditional methods were not successful. The test vehicle used in this study was a highly complex customer server product which was under development.
Key words: Lead Free Server, High Complexity, PTH Rework, Product Vehicle, New Rework Methodology
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