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February 2000

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Tue, 29 Feb 2000 12:56:35 -0800
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Louis,

Go to site www.rampinc.com, then to search and browse thru Free Paper Downloads. Here
you can search for Palladium Plating. The list should be 2-3 papers. When you click,
you will go to TI site for that paper. Print or browse. Good Luck.

"Louis, Edwin @ CSE" wrote:

> After some problems here with cracked solder joints on Alloy 42 leaded TSOP
> devices, our stress analysis expert did some calcxulations And found that
> the stress were above yield strength for the SN63 solder but not by much. We
> sent some of the devices back to the manufacturer for their testing and they
> found solder joint pull forces necessary to break the lead/solder bond to
> be between  0.33 Kg and 0.78 Kg. The former is 0.726 lbs  and the latter is
> 1.716 lbs. We are talking about fine pitch 19 mil.
> Some one in  the assembly business said that between 1.0 and 1.5 lbs pull is
> expected. These alloy 42 leads had a tin/lead (high lead composition)
> plating which was not reflowed. My experience shows has been that tin/lead
> plating has to be reflowed in order to be
> a protective film. This type of plating is very porous and the lead oxidizes
> easily. I hear reports from some quarters that alloy 42
> TSOPs are used successfully and others say never use alloy 42 TSOPs they
> don't work. We encountered a manufacturer who used identical TSOPs as we
> used but did not complain about any problems. The difference was that they
> assembled the parts as soon as they arrived. We did not. Our solder joints
> showed cracks at the heal hours after soldering. Reflow of our stressed
> joints
> manually, using RMA flux, alleviated the problem. I am thinking here that
> the alloy 42 TSOP problem is caused partly by solderability
> and partly by coefficient of expansion mismatch. I have heard that some
> people are changing to palladium or palladium/silver
> plating to overcome solderability problems. Can some one tell me where to
> learn about these platings and are they worthwhile
> pursuing.
>
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--
____________________________________
Regards,
Pratap Singh

Tel./Fax: 512-255-6820,
e-mail: [log in to unmask] or [log in to unmask]

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