Depending on the type of X-Ray machine used it might be the way the X-Rays are being generated or processed. We have machines similar to what airports use and the image is skewed as the X-Rays are a point beam and are fanned out diagonally to the vertical and horizontal receptors that are located diagonally opposite the source, this is to provide a somewhat 3-D view of the object being scanned.
Pat
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, February 22, 2013 5:33 PM
To: [log in to unmask]
Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem.
Hi Alan,
Sorry about the delay, but I got your pictures posted. The links are here:
http://stevezeva.homestead.com/QFN_48_pin_pry.jpg
http://stevezeva.homestead.com/QFN_48_pin_reflow.jpg
http://stevezeva.homestead.com/QFN_48_pin_x-ray.jpg
I can't tell a whole lot from the pry.jpg or the reflow.jpg image, but the x-ray image does intrigue me.
To me, it looks like the QFN was tilted when the x-ray was done. It looks like it was tilted down at the upper left hand corner with the lower right hand corner sitting higher.
I say that because if you look at the solder spread on the pads, it seems to be more consistent along the left hand side than it does anywhere else on the device. I also see that there seems to be a blob of solder on the thermal pad down in the lower right hand corner. Also a lot of voids in the thermal pad area...more than I would like to see.
The solder on the rest of the pads seem very inconsistent...doesn't look like that would result from a paste print and reflow. Do you know it this part was reworked ? To me it looks like was...
Steve Gregory
-----Original Message-----
From: Alan Young
Sent: Friday, February 22, 2013 2:34 PM
To: [log in to unmask]
Subject: RE: [TN] 48-pin QFN via-in-pad solder slug problem.
Hi Steve,
Would it be possible to host these images for a discussion that is going on at the moment?
Many thanks,
Alan Young.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Friday, February 22, 2013 2:28 PM
To: [log in to unmask]
Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem.
Alan,
Technically, IPC rips off any attachments you might try to add.
Send Steve Gregory a note at [log in to unmask] To see if he has the time to post them on his site.
Alternatively, you can go to the IPC site, sign in, and create a folder of your own that all can see if you send us the link.
Regarding the solder slug on the underside of the device. I don't believe
you explicitly stated that you saw evidence of solder wetting to it.
Couldn't it be that the copper slug just isn't getting warm enough for the
solder to wet to it and the solder preferentially decides to wet to the
warmer vias? Follow along with what Ted said.
Snowbound sparrow - west MI
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Alan Young
Sent: Friday, February 22, 2013 2:12 PM
To: [log in to unmask]
Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem.
Thanks aging for all of this feedback, really appreciated!
Is it okay to attach some images to an e-mail or can I send some to somebody
so that they might be able to host them?
Alan.
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, February 22, 2013 1:26 PM
To: [log in to unmask]; Alan Young
Cc: [log in to unmask]
Subject: RE: [TN] 48-pin QFN via-in-pad solder slug problem.
A picture is worth one thousand words.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Alan Young
Sent: Friday, February 22, 2013 11:23 AM
To: [log in to unmask]
Subject: Re: [TN] 48-pin QFN via-in-pad solder slug problem.
Hi folks,
Please forgive me if this topic does not belong to this group.
Let me explain my predicament.
I'm a PCB layout guy who has been asked to look at a soldering issue we are
having with a 48-pin QFN 7mmx7mm [EMBER CORP - EM357-RTR], the solder slug
under the part is not soldering/bonding to the PCB. The pcb footprint is
made per the manufactures specification with a 5.3mm x 5.3mm solder slug pad
with 9 vias finished drill size of 0.254mm. There are no soldermask features
on the component or solder side over the vias.
When the board has been reflowed, all of the 48 pins solder well but the
slug has not bonded to the pcb. There are signs of solder in the slug vias
on the opposite side of the board. If the part is ripped off the board, the
slug is clean and solder free.
I do not have any information about the paste screen setup or the oven
profile.
The questions I have are;
1 - Any ideas on why this is happening?
2 - Are the vias in the slug causing this problem?
3 - Would soldermaks capping the vias on the component side help resolve
this?
4 - Would plugging (no capping) of the vias with epoxy help?
5 - Do north African sparrows fly faster then European sparrows (just seeing
if anybody is reading this :-)
I do have some photos and x-rays of the device if this will help.
Again any help or comments would be greatly appreciated.
Regards,
Alan Young.
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