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August 2009

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From:
stephengregory5849 <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, stephengregory5849 <[log in to unmask]>
Date:
Mon, 10 Aug 2009 08:38:44 -0500
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I can tell you that the application note that Actel puts out for their 
QFN180 is worthless. The reduction for the thermal pad that GA Tan is in the 
ballpark, might even be a little too much. The problem with this part is 
that there is such a razor thin balance between figuring out how much paste 
you print for the thermal pad and getting decent I/O pad joints. The three 
row I/O pad pattern make things all the more difficult. We were dealing with 
single and double row QFN's without any problems until we ran across this 
beast.

Oh, as far as trying to rework the part, good luck! It ain't happening. We 
even paid a company who does nothing but rework for a living to try and 
rework the part and it gave them fits. They were able to get the part back 
down after much difficulty, but the board never worked. Don't know if the 
part died during rework or if it was something else. Just know it wouldn't 
program when we got the boards back.

Steve

----- Original Message ----- 
From: "Tan Geok Ang" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, August 10, 2009 2:24 AM
Subject: Re: [TN] Actel QFN180 Assembly


Hi Grivon,
               There is some guide from Actel : 
http://www.actel.com/documents/QFN_AN.pdf which I don't think it will work 
well. Go for a volume of 55% at the thermal pad (and a pad opening of 9mils 
(5mils stencil thickness) with slight rounded radius at the corner of the 
opening. What is your problem and stencil openings? With your result, you 
will able to know where gone wrong. FYI, we used only two rows of QFN as of 
now and lots of LGAs. Hope it help.

Regards
GA Tan

________________________________

From: TechNet on behalf of GRIVON Arnaud
Sent: Fri 8/7/2009 6:04 PM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly



Coming back on an old post from Steve (at his former employer...).
Does anybody have good stencil rules for the assembly of multi-row QFNs and
especially triple-row such as ACTEL QFN180?
Like Steve and probably many others, we tried to find the right aperture
balance between I/Os and central thermal pad without success...
A. Grivon

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