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November 2008

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TechNet E-Mail Forum <[log in to unmask]>, Andy Ng <[log in to unmask]>
Date:
Thu, 20 Nov 2008 12:35:28 -0800
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We worked with our vendor once on a low temp alloy 58Bi/42SN from  
Indium for a QFN that cannot withstand the eutectic and peak of SnPb  
solder. Not sure if they do sell in cored wire, and if it is  
compatible with SnPb, but the MP and peak are 140C and 175C, and it  
showed pretty good wetting.

On these LEDs, might also want to be extra careful on the handling.  
Wearing gloves and never using tweezers to pick up from the lens can  
extend the life.

Andy

>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Wednesday, November 19, 2008 11:50 AM
> To: [log in to unmask]
> Subject: [TN] Low temp solder alloy
>
> Dear Technos,
>
>
>
> I have another one for you.
>
>
>
> We do these boards having 100 to 200 TH high power LEDs (5mm in
> diameter) and see a fairly high return since after a few weeks in the field
> some LEDs will die or become intermittent. So we sat down and started
> reading the app notes, see an example at
> http://www.cree.com/products/pdf/LED_Lamp_SolderingHandling.pdf
>
>
>
> Well, it turns out that these components cannot be touched up with solder
> irons at more than 280C, which is 530F. This is rather low and I wonder if
> we are going to be able to get the solder up the hole.
> Anyways, I am heading towards the shop, in order to do some testing.
>
>
>
> In the mean time, I would like to have your opinion on low temp alloys I
> could use for touch-up:
>
> o        What alloy should I look at?
>
> o        Can I use a low temp alloy to touch up eutectic SnPb joints?
> Any compatibility / reliability issues related to the eventual mixture?
>
> o        Any particular low temp alloy that is more compatible with
> SnPb?
>
> o        Anything else I should think about?
>
>
>
> Thanks again,
>
>
>
> Ioan
>
>
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