Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Solder short-BGA with thermal pad

haran

#22856

Solder short-BGA with thermal pad | 27 December, 2002

Currently we are running a BGA with a big thermal pad in the middle of the package and encountered high defect of solder shorts.I would like to check whether anyone has experience this problem and how this can be rectified?.

reply »

#22858

Solder short-BGA with thermal pad | 27 December, 2002

what exactly do you mean by big thermal pad?

reply »

haran

#22859

Solder short-BGA with thermal pad | 27 December, 2002

Big pad located at the middle of the package. On the PCB,we need to have solder paste printed on the thermal pad which is at the middle and the other pads of the perimeter BGA.

reply »


CPI

#22861

Solder short-BGA with thermal pad | 27 December, 2002

We have placed these parts. I have not had problems with them but when I designed the stencil we reduced the app for the large thermal by 20% to reduce the chance of problems like your having. If the balls are close (.040-.050" or <) to the pad I would reduce the app in the stencil by at least 20%. When the BGA is placed there will be a little squeeze out, once the balls collapse there will be even more. You may also want to use a stepped stencil to apply less paste on the thermal pad land.

reply »

#22865

Solder short-BGA with thermal pad | 28 December, 2002

If the problem is in the big thermal pad.The surface strains in that pad are different then the others and through the reflow period there is an affinity between them(only if they are too close). I recommend you to reduce the theramal pad. Make smaller print.

If the pads are not so close to the big one : -too much solder paste -a print with irregular form (the print finishes with a tail ,the print is inclined or something like that) -too long in the reflow zone -bad aligment in assembly (much pressure, rotation, bad aligment x, y) -manual operation (if there is any)

It's not much, but it might be one of these.

reply »

#22872

Solder short-BGA with thermal pad | 30 December, 2002

Haran, This problem can also be caused if the BGA package is POPCORNING. Popcorning causes the BGA package to expand below the die, seen this happen so often to customers that try to install BGA's themselves without the proper handling of BGA's.

Thanks

reply »

Arturo

#23419

Solder short-BGA with thermal pad | 18 February, 2003

Our case is not due to thermal pad print squeezing because our shorts are mostly in the outer rows of the BGA so they cannot be caused by central pad printing. We still stick to the BGA thermal pad coplanarity/height hypothesis but have not yet proved that.

Arturo.

reply »

#23420

Solder short-BGA with thermal pad | 18 February, 2003

Arturo,

So, you're not shorting to a thermal pad.

Given that you're shorting to outer balls, tell us about: * Location of the shorting among the outer balls. * Board construction. * BGA constuction. * Paste deposition. * Temperature measurements taken on these balls during reflow and how you went about taking these values.

Finally, help us understand more about your "BGA thermal pad coplanarity/height hypothesis".

reply »

Arturo

#23428

Solder short-BGA with thermal pad | 19 February, 2003

Is there any way I can attach a report?

reply »

#23434

Solder short-BGA with thermal pad | 19 February, 2003

We usually end-up emailing reports and pix to each other. Fire a copy off to me.

reply »

reflow oven profiler

PCB Soldering Tools