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June 2007

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Subject:
From:
Nila Young <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Nila Young <[log in to unmask]>
Date:
Thu, 14 Jun 2007 17:03:43 -0600
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Hi John,

As for the process, yes, I think you have it right on what we want to
do. But, I have to be able to actually state it on the drawings so that
there are no questions asked when we send it to what ever printed
circuit board vendor that purchasing specifies.  

Here is where the problem occurs. Purchasing folks want to use our
supplier in China, not our sister company's supplier because of cost and
lead time. There is a supplier here in the USA that can do this for us,
but again, purchasing folks are not wanting engineering to pursue this
alternative for cost savings reasons. Sigh. 

I did get the notes directly from our sister company as they have a
similar pcb that has more LEDs on it than what we want. So not much help
there as to improving things as that is the only mcpcb that they have.

Now why to assemble directly on aluminum.... The LEDs that we want to
use need to be in a very confined area so not enough room for a separate
heat sink or to use plane layers to act as a heat sink as the pcb would
then not fit in the housing. By mounting them directly onto aluminum,
the heat sink and the pcb are one, and the pcb area can then be greatly
decreased. 

Thanks :-)
Nila

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Thursday, June 14, 2007 4:46 PM
To: [log in to unmask]
Subject: Re: [TN] MCPCB finish questions

OK this is driving me crazy.

In 1985 I printed a Budweiser can with a clear coat followed by
conductive traces and stuck down led's using conductive epoxy, this
worked really well.
The same year I assembled enamel coated steel boards with LED's

For your LED board I strongly suggest you use the same approach - treat
it like you would a hybrid and print down the circuitry.

And if you want to get right down to it pick up the phone to your sister
company and ask where they get them made.........8-).

And I guess the question everyone would be thinking is why you would
want to assemble onto aluninium?


 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nila Young
Sent: Thursday, June 14, 2007 3:31 PM
To: [log in to unmask]
Subject: Re: [TN] MCPCB finish questions

Werner,

The sample I have from our sister company does not have metal surrounded
by 2 pcbs. It is a real metal pcb that is intended to act as a heat sink
for the leds and is not surrounded by any FR-4. (Yep, a soldering
nightmare that I am sure plenty of assembly personel will be happy to
work on...) It is just a piece of aluminum that has a coating on one
side with traces laid on top of that followed by a soldermask. We will
not be putting the leds on ourselves, but will look for a cm to assemble
it. I believe that our sister company may have a CM that is hand
soldering the leds to the mcpcb. The only other part that goes on this
is a connector that will connect a FR-4 pcb to drive the leds. 

As for your White Paper, I have not read it as our pcbs are typically
all through hole and our engineers are just now in the process of
converting to RoHS compliance. 

Nila

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, June 14, 2007 4:18 PM
To: [log in to unmask]
Subject: Re: [TN] MCPCB finish questions

Hi Nila,
Your PCB sounds like a "challenge"-not to say nightmare in this brave
new LF-world of ours.
I sure hope you are planning on using vapor phase for your solder
assembly process, otherwise the thermal requirements are going to be
"hellish".
When you say 'metal core', do you mean a real metal-core substrate, or a
PCB 
with a heat sink   in the middle surrounded by 2 FR-4 PCBs?
What are you doing to make your PCB survive the LF-assembly process?
Did you read my White Paper on the subject?

Werner



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