When I worked as process analyst many years ago, I loved this kind of
problem, because we could  live for days on the task. . You should know
that driving such a lab doesn't make you rich!

While I write, the many responses may already given you help.

The way you pry is not what I'm used to see. Looks like a massacre. You
need pray for a better pry. I use different way, not saying it's perfect
either, but could be worth testing. I dip the board sample in LN2 until
equilibrium, then lock it in a vise standing vertically. By means of a
steel bar, rectangular, flat ends, I give the package a knock parallel with
board. At that low temperature, the solder is brittle and the packages use
to jump off easily. Not applicable on large
packages.

Can you do some good cross sections, polish them and fine etch for some
seconds? An hour or two will it take, but will tell much more to us than
the pry samples. After that we are all ready to give more precise advice.

Have you checked the solder pads for 'bumps' under the tinned surface.
Bumps from via fills can cause the whole package to ride so much higher,
that the solder slug does not make physical contact with the board¨s site.

Have you checked the coplanarity and the distance between the two planes,
slug plane and I/O plane?

Have you correct time/temp for preactivation of flux and evacuation of flux
solvents? If too much volatils are left while the assembly goes into peak
zone, the gas generation can be so violent that the package begins to hop,
and you lose control of where the solder goes.

Have you done the simple water drop test to get basic idea of how good the
slug wetting is?

Have you done the simple test with a small weight on top of the package
before it goes through  the oven?

Have you checked that the board isn't shaking under the soldering process?

Can't say more as you have only presented the pry photos


Best  wishes /  Inge


On 22 February 2013 18:23, Alan Young <[log in to unmask]> wrote:

> 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.
>

    I got a rather good soldering instruction from a friend at Infineon.
Read it. May find a nugget? >Dropbox.com>Reports for Technet >
 Solderability > Soldering Instruction Infineon

>
> Regards / Inge
>

PS Think Steve Gregory is on the right direction

>
> Alan Young.
>
>
>
> This e-mail message and all attachments transmitted with it may contain
> legally privileged and confidential information intended solely for the use
> of the addressee. If you are not the intended recipient, you are hereby
> notified that any reading, dissemination, distribution, copying, or other
> use of this message or its attachments is strictly prohibited.
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________