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November 2008

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
Date:
Thu, 20 Nov 2008 06:27:55 -0500
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text/plain (83 lines)
I saw this in an application where the LEDs were mounted flush with the
board. So, the PTH was in contact with the base of the LED. This resulted in
internal damage to the device and the kind of failures you describe. 

We recommended an unsupported hole. The board was redesigned. Component
remained flush mounted but with a single pad on the solder side there was a
1.5 mm gap, no requirement for vertical fill and a relatively easy solder
connection. Latent failures dropped to near zero. 

-----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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