Influence of temperature and humidity on printed wiring board surface finishes. Immersion tin vs organic azoles
- AT&T Bell Lab., Princeton, NJ (United States)
- Sandia National Lab., Albuquerque, NM (United States)
Substitution of lead-free solders in electronic assemblies requires changes in the conventional Sn:Pb finishes on substrates and component leads to prevent contamination of the candidate lead-free solder. Options for solderability preservative coatings on the printed wiring board include organic (azole or rosin/resin based) films and tin-based plated metallic coatings. This paper compares the solderability performance and corrosion protection effectiveness of electroless tin coatings vs organic azole films after exposure to a series of humidity and thermal cycling conditions. The solderability of immersion tin is directly related to the tin oxide growth on the surface and is not affected by the formation of Sn-Cu intermetallic phases as long as the intermetallic phase is underneath a protective Sn layer. Thin azole films decompose upon heating in the presence of oxygen and lead to solderability degradation. Evaluations of lead-free solder pastes for surface mount assembly applications indicate that immersion tin significantly improves the spreading of Sn:Ag and Sn:Bi alloys as compared to azole surface finishes. 14 refs., 9 figs.
- Research Organization:
- Sandia National Laboratory
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 81366
- Report Number(s):
- CONF-940204--
- Journal Information:
- Journal of Electronic Materials, Journal Name: Journal of Electronic Materials Journal Issue: 8 Vol. 23; ISSN JECMA5; ISSN 0361-5235
- Country of Publication:
- United States
- Language:
- English
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