It's remarkable how little is written about the art of hand soldering. Yes,
it IS an art!
We have some old guys who know how to solder properly. The younger rotate so
often,
that they will never be soldering masters.
We do LED tru (sorry Mike, american) hole soldering this way.
1. Never pretin the hole.
2. Always pretin the tails
3. Dispense solder past on the site (186 Celcius paste)
4. Use I.C. tip with extra long body
5. Fresh cleaning cusion and deionised water
6. Apply an extra drop of flux immediately before soldering
7. 300 Centigrade tip, fast soldering, max 3 seconds
Well, that's our way...there are certainly better ones
Inge
----- Original Message -----
From: "Rex Waygood" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, November 20, 2008 12:38 AM
Subject: Re: [TN] Low temp solder alloy
It strikes me that whoever wrote the hand soldering spec either doesn't
understand hand soldering or is doing a CYA.
In doing the rework I would ignore the 35W 'command' as that will just
get you into difficulties. 280C from a 90W iron is the same 280C as from
a 35W iron but my guess is time for soldering with a 90W iron will be a
lot less than a 35W iron and therefore potentially less damaging. If
Cree are making assumptions about thermal impedance of a 35W vs a larger
iron they are in dangerous territory (35W laser?). I would preheat the
board assembly prior to reworking with the iron to the maximum you think
you can get away with.
If you wanted to be really clever and enthusiastic you could calibrate
the 'Vbe' of the led vs temp and monitor that during a rework to
characterise your process. Making connection would require a bit of
inventiveness! :-)
More of interest, why are the leds failing?
Rex
Rex Waygood
Technical Manager
PartnerTech Poole Ltd
Benson Road
Poole
Dorset BH17 0RY
United Kingdom
Tel: +44 (0)1202 674333
Fax: +44 (0)1202 678028
DDI: +44 (0)1202 338222
Mob: +44 (0)7887 997403
[log in to unmask]
www.PartnerTech.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: 19 November 2008 16:50
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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