Solderability perservative coatings: Electroless tin vs. organic azoles

Conference · Thu Jul 01 04:00:00 EDT 1993

OSTI ID:10172107

Artaki, I; Ray, U; Jackson, A M; Gordon, H M ^[1]; Vianco, P T ^[2]

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1. AT and T Bell Labs., Princeton, NJ (United States)
2. Sandia National Labs., Albuquerque, NM (United States)

This paper compares the solderability performance and corrosions ion protection effectiveness of electroless tin coatings versus organic azole films after exposure to a series of humidity and thermal (lead-free solders) 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 protected by a Sn layer. For a nominal tin thickness of 60{mu}inches, the typical thermal excursions associated with assembly are not sufficient to cause the intermetallic phase to consume the entire tin layer. Exposure to humidity at moderate to elevated temperatures promotes heavy tin oxide formation which leads to solderability loss. In contrast, thin azole films are more robust to humidity exposure; however upon heating in the presence of oxygen, they decompose and lead to severe 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.

• Research Organization: Sandia National Labs., Albuquerque, NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 10172107
• Report Number(s): SAND--93-1414C; CONF-9308126--2; ON: DE93017634
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
426000
AZOLES
COMPARATIVE EVALUATIONS
COMPONENTS
ELECTRON DEVICES AND CIRCUITS
HUMIDITY
MATERIAL SUBSTITUTION
METALLURGICAL FLUX
PRINTED CIRCUITS
PROTECTIVE COATINGS
SOLDERING
TIN
WETTABILITY