To Andy
Sounds like you either need to use some type of preheater, baking oven or hot plate for Prototypes. Consider a Selective solder system for volume where the board is preheated by a preheater or by the hot nitrogen as it solders the leads. I'm assuming you aren't wave soldering them. With a wave solder system with Tin/Lead you'd only need 485F for a board 0.062"thick, 490F if .092" thick. For Pb-free you will be up to 510F to 530F depending on the thickness of the board.
If you need info on any of the above I'll be glad to provide you with the information.
John
Sr MFG Engineer
-------------- Original message --------------
From: Andy Ng <[log in to unmask]>
> 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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