Yes. That joint wasn't monitored, but it was there. 3mm center pad for the 32 pin, 5 mm for the 48, and 6 mm for the 68 pin. All the parts had representative die that were the maximum size allowed for the package size.
On the subject of center pads, I did a test once where I purchased the same package with 3 different sized center pads. Identical package outline and identical die, the only difference was the center pad size. The pad on the board side was 1:1 with the package side with a grid of vias as would be typical in a real design. Interestingly, the larger the center pad, the sooner the perimeter joints failed. I don't remember whether they were QFNs or exposed pad TQFPs and I can't find where I put the data at the moment - several computers have come and gone since then.
Scott Post
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana 46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, April 03, 2012 2:52 PM
To: TechNet E-Mail Forum; Post, Scott E
Cc: [log in to unmask]
Subject: Re: [TN] how to pass solder joint reliability of a 3.2 mm board (16 layers) for QFN packae
Hi Scott - in your testing trials, have the QFNs had center pads (aka thermal/grounding pads) which were soldered down to the assembly?
Dave
"Post, Scott E" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
04/03/2012 01:25 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Re: [TN] how to pass solder joint reliability of a 3.2 mm board (16 layers) for QFN packae
100,000 cycles of -55/+125C? Did the parts have representative die in them?
Scott Post
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana 46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Tuesday, April 03, 2012 2:24 PM
To: [log in to unmask]
Subject: Re: [TN] how to pass solder joint reliability of a 3.2 mm board (16 layers) for QFN packae
Can you develop your question so that a slow thinker like me can understand
TMCL 1000 c on QFN8's is very mild, I suppose nothing will happen. I
investigated QFN64's recently. They had passed 100,000 cycles with some few
issues. This was a -55/125 C test.
I think you should tell a little about the assembly, because that's what
decides the result.
Inge
On 2 April 2012 18:55, jonathan noquil <[log in to unmask]> wrote:
> Hi All
>
> Need some suggestions on how to handle solderjoint issue (How to tweak to
> pass TMCL1000 cycles- 0 to 100C) on QFN packages ( 5 x 6 x 1.0 mm with 8
> pins).
> Finish is Pure Sn
> Board is 16 layers 3.2 mm, HASL finish.
>
> Does someone had an experience to share?
>
> thanks
>
>
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