Hey Steve ; do you ever take a break ?
I don't thing we're as much as bosses slaves as being sucked in by this
leaching industry :
we'd suffer from stress starvation fits ; would we move to anything else !
Where were we ?
Yes : how do you, ol' salt, manage to burn TH LED's ; ( not mentioning SMD's
; that I could swallow ) ?
Also : Tom is driving good point = if you burn "some" > "obviously" ; bet
your life that the rest will not live happily there and after .
He's also pointing the usual mistake of overcurrent stress ; you wouldn' do
THAT ; would you .
What I noted in all of the brands ( you name them ) ; the component
construction is very much on limits with heat habits ( like top preheat ) of
traditional process ;
and most of the LED makers did have a problem ( overcomed just recently ) to
come up with inherently reliable concept .
So ; on TH :
Switch of top preheat ; keep bottom "just" to dry the board ; and baring any
big heat suckers (sink mounts) you may have to "touch up" after : keep the
pot on 240'C .
Keep both ends of wave open to keep the air cool ( presume bottom IR ? ) .
We've sat all of our TH LED's straight on board (with bigger holes to let
the stand off kinks through) : no problem if you keep it cool .
If you top preheat to keep your barrels nicely full & shiny (customers love
it , hey ?) ; you kill 'em ( the LED's I mean ) ; bottom only preheat is
(looking at profiles now : > tops 150'C) !
No shorts, dry's, ball's & bull's ; as they (A) say ; on NiAu ; on HASL you
should have it easy .
I found the top notch waves with all of the heating blow's & w's have much
more problems to keep LED's alive than the simple fry pan pass pots .
On SMD :
Apart from above ; often the construction is inadequate ; I have to mention
for example Tenrod folks when we pulled one of their older design LED's
through my (as usual) obsessively cool process and it still was not enough :
I bitterly objected ; they grudgingly admitted field problems due to design
limits > pulled all of old stock out ; came to the party ; replaced it with
new more robust design and all's well even on reflow :
I was impressed how well > appropriately the guys were commercially
motivated ; the speed of info's back and forth was hours , not days ; with
two eng's with me .
That is ; watch their specs ( apart from they're impossible to keep most of
the time ) they're on limits as well ; and they know it to .
We're all in the limit game ; LED's more than cap's .
That's it ; you dedicated ; hard working .........; geeze all right
!...............
Hey ; did you hear it's easier to think hard than to work hard
.....?......hehehe........
Kidding Steve ; I actually ( been there ) know the sub guys like you are the
most agile ( not like us OEM's ) ;
sometimes the comps coming for assembly were just ripe for sandblasting ( no
acid would touch it ! ) ; and the variety of problems (one day in and never
again) more or less precluded any SPC full stop ; whenever I'm hiring : the
sub (contract) lads have preference .
Usually they've seen it all ; apart from new technologies .
See you mate ; stay cool
Paul Klasek
http://www.resmed.com.
> ----------
> From: Stephen R. Gregory[SMTP:[log in to unmask]]
> Sent: Wednesday, 30 December 1998 6:09
> To: [log in to unmask]
> Subject: [TN] Assy: LED Failures...
>
> Hello der' Everybody!
>
> Well, judging from the amount of email I've been getting from the
> TechNet
> server, looks like there's only a few of us dedicated, hard-working people
> who's forgoing the holiday spirit in order to support our nations
> electronic
> needs... 'scuse me for a minute...(Geeze, did I lay that on thick or
> what?...GRIN)
>
> Actually, it's probably more like those of us that are still here, have
> slave
> drivers for bosses...(glad mine doesn't read the TechNet! hehehe...)
>
> Anyhoo, I'm building some little Ethernet 10Base Fiber Transceivers, and
> they
> have a series of 5 LED's on them. Problem is, they're dying like flys
> through
> the process. That's been our biggest failure at test...in fact, it's been
> about the ONLY failure we've had. Seems I 'member someone saying something
> about LED's being a part that doesn't do well through assembly, that it's
> just
> the nature of LED's. Is that true? (I think it was Paul Klasek from
> Resmed...Paul, was that you?) Is there anything that I can do differently
> that
> might baby them a little more and help them survive? I didn't account for
> having to change a good percentage of them in my labor quote...which is a
> bummer, we're not making much on this deal.
>
> Thanks in advance, all you work-a-holics!
>
> -Steve Gregory-
>
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