Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

CTE mismatch

Serrena Carter


CTE mismatch | 14 September, 2000

Does anyone know where I can find good rule of thumb information on soldering/brazing. I am most interested learning the maximum recommended CTE mismatch between two different materials that thermally cycle between 25-100C.

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Re: CTE mismatch | 15 September, 2000

Sounds like someone aimin� fo tha big hurt, if ya axes me. Two spots to place your lawn darts are: 1 J Hwang in "Modern Solder Technology � " states (p.354) that " � extreme CTE mismatch between silicon IC (~2) and the PCB (~16), solder connections of this package are expected to undergo adverse stress during the service life." 2 J Lau and Y Pao in "Solder Joint Reliability � " state (p.332-3) "Comparing the thermal coefficient of expansion of the TSOP body ax [6.7 ppm/�C] and az [9.8 ppm/�C] and the PCB (a=15 ppm/�C), the difference (global thermal expansion mismatch) is very large. Furthermore, the lead frame material of the TSOP was made of alloy-42 with a 300-microinch thick (7.62 microns) 90wt%Sn-10wt%Pb plated surface. The thermal coefficient of linear expansion of alloy-42 was 5 ppm/�C. Thus, the thermal expansion mismatch between the gull-wing lead and the Sn/Pb solder joint (21 ppm/�C) is quite large.

A young Yankee gent meets a comely Southern lass. In the midst of their small talk �

yYg: There are certainly some good universities down here in the South, but there�s some good ones in the North, also. cSl: Ah do believe you�re correct. Where dijall go to schoo up Nuth? yYg: Yale cSl: WHERE DIJALL GO TO SCHOO UP NUTH?

Have a nice weekend

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