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May 1998

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From:
"Yuen, Mike" <[log in to unmask]>
Date:
Fri, 1 May 1998 09:30:00 CDT
Reply-To:
"TechNet E-Mail Forum." <[log in to unmask]>, "Yuen, Mike" <[log in to unmask]>
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Beside gold thickness, the amount of solder applied should also be
considered.  Per IPC-D- 279, "Design Guidelines for Reliable Surface Mount
Technology Printed Board Assembly",  Section 5.4.4.  where gold or palladium
plating is used, the gold or palladium content in the solder joint should be
approx 3 %wt. or less.  Here are our thinkess rules for Gold.

Electrolytic AKA hard gold: Mostly for Wire bond
Elecrtroles AKA Soft gold: Common 15 to 25 u" as long as it follows the 3%wt
rule
Immersion: Common 5 to 10 u" (Preferred in SMT assemblies, except edge
finger connector)

To calculate the weigth factors, these number might help
     Density of Gold =        19,300 kg per m3
     Density  of Solder  =    8,500 kg per m3

Please ensure to have at least 100 u" of Ni beneath the gold.


Hope that helps
Michael Yuen

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