Wetting characteristics of Pb-free solder alloys and PWB finishes

For a successful transition to Pb-free manufacturing in electronics assembly, it is critical to understand the behavior of Pb-free solders (in bulk and paste form) and their interaction with the Pb-free printed wiring board (PWB) finishes. This paper presents the results obtained from solder paste s...

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Bibliographic Details
Published in:IEEE transactions on electronics packaging manufacturing 2002-07, Vol.25 (3), p.168-184
Main Authors: Sattiraju, S.V., Bing Dang, Johnson, R.W., Yali Li, Smith, J.S., Bozack, M.J.
Format: Article
Language:English
Subjects:
Alloys
Applied sciences
Assembly
Circuit boards
Design. Technologies. Operation analysis. Testing
Electronic equipment and fabrication. Passive components, printed wiring boards, connectics
Electronics
Exact sciences and technology
Finishes
Integrated circuits
Lead base alloys
Manufacturing
Microelectronic fabrication (materials and surfaces technology)
Nitrogen
Performance evaluation
Printed circuits
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Sequential analysis
Solders
Spectroscopy
Spectrum analysis
Spreads
Studies
Surface finishing
Testing
Tin
Wetting
Wiring
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Summary:For a successful transition to Pb-free manufacturing in electronics assembly, it is critical to understand the behavior of Pb-free solders (in bulk and paste form) and their interaction with the Pb-free printed wiring board (PWB) finishes. This paper presents the results obtained from solder paste spread tests and wetting balance experiments with several Pb-free solder alloys and Pb-free PWB finishes. The solder alloys studied were Sn3.4Ag4.8Bi, Sn4.0Ag0.5Cu, Sn3.5Ag and Sn0.7Cu. Eutectic Sn37Pb was used as a reference. The PWB surface finishes were Sn, NiAu, Ag and OSP. Wetting balance experiments were conducted in air while the spread tests were performed in air and nitrogen to understand the effect of reflow atmosphere on the spreading. Surface analysis techniques such as Nomarski phase contrast microscopy, Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to characterize the as-received PWB finishes. Sequential electrochemical reduction analysis (SERA) was also performed on the as-received PWB test coupons and on the Sn test coupons after multiple reflow cycles. The effect of multiple reflow cycles on the wetting performance, spreading and the surface composition of the PWB finishes was studied.
ISSN:1521-334X
1558-0822
DOI:10.1109/TEPM.2002.801651