We had a similar experience with a QFN MEM. The recommended pad had
copper but no resist under the part, had a centre pad on the part and an
instruction that the device would not function correctly if the centre
pad was soldered to the PCB.
Regards
Rex

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: 19 April 2013 16:52
To: [log in to unmask]
Subject: Re: [TN] QuickFilter 16-pin VQFN

Hi Steve - I have ran into a similar case where a MEMs device  was put
in a QFN style package. The QFN center pad was not soldered as it would
make the MEMs device nonfunction (aka the bottom of the QFN package
soldered to the assembly made things so rigid that the MEMs didn't
function correctly). I understand why we couldn't solder the center pad
but yes, it was hugely confusing to the process folks as here was pad
that we always solder and were not - everyone kept thinking there as a
mistake.

Dave Hillman
Rockwell Collins
[log in to unmask]



From:   Steve Gregory <[log in to unmask]>
To:     <[log in to unmask]>
Date:   04/19/2013 10:10 AM
Subject:        [TN] QuickFilter 16-pin VQFN
Sent by:        TechNet <[log in to unmask]>



Good morning all,

 

I've been looking at a board that we will be building in several weeks,
and one of the packages on the is a 16-pin VQFN. Part number is:
QF1D512-QN-T. Datasheet is here:

 

http://www.quickfiltertech.com/files/QF1D512%20SavFIRe%20Datasheet%20A15
.pdf

 

I always check the datasheet to look at the recommended solder paste
footprint to ensure that the stencil I spec out falls within the
manufacturers recommendations. Yeah I know that sometimes the
manufacturers footprint doesn't always work, but I look at it anyway for
a sanity check.

 

Well, the datasheet doesn't have one, and I sent a contact email to
QuickFilter asking if they had a recommended solder paste footprint for
this part and didn't receive a reply, so I called them the next day.
When I spoke with them I was told that they didn't have a documented
footprint for the part, but there was one thing they wanted me to know,
which was to NOT print solder paste for the center pad beneath the part.
"But why?" I asked, "there's a pad there in the drawing of the part...".
I was told that the pad is completely non-functional, and the reason
that it's there is because they didn't want to have to come up with a
custom lead frame for this part, and this was the lead-frame that was
"off-the-shelf" and what was used.

 

Well, I was surprised! I mean this does make things easier for assembly
by not having to worry about soldering the center pad, but this is the
first time I have ever ran across something like this. Have any of you
ever run across this on any other QFN parts?

 

Have a good Friday everybody!

 

Steve Gregory

Process Engineer

Kimco Design and Manufacturing

652 N. Five Mile Road

Boise, ID 83713

(208) 322-0500 Ext. 3133

 


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