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Solder briding on QFP

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Happy New Year to All: Has anyone of you encountered a sold... - Jan 08, 2010 by graceyt  

so good ... - Jan 25, 2010 by Steven(Ludee Circuits)  

#60794

Solder briding on QFP | 8 January, 2010

Happy New Year to All: Has anyone of you encountered a solder short on QFP pin yet there's no evidence of bridging in between gaps? I am using an SnPb solder paste.

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#60801

Solder briding on QFP | 8 January, 2010

Not specific to QFP, but I had a run of poorly etched boards. I could see the short using 75X magnification with back lighting, but only some of the time. Nasty little shorts on ~25% of the boards that cost us a boat-load of cash.

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#60802

Solder briding on QFP | 8 January, 2010

Thanks for the reply. I'll try your suggestion. I tried the SEM EDX to check for traces that might cause the bridging problem but it looks normal. I haven't tried yet the material level analysis of the QFP. Thanks again.

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#60805

Solder briding on QFP | 11 January, 2010

In a former job we had issues with leakage currents on a QFP. The component was acting as a thermal shield leaving a lot of flux residue behind. To make it worse, the flux solvent wasn't totally evaporated, so we had ionic residue, a fluid media, and a voltage difference. We got leakage currents. We eventually had to change the board design to help eliminate the solvent and help activate the flux. Even with that, we still got a few returns.

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#60808

Solder briding on QFP | 11 January, 2010

are you seeing this post processing or are they coming back from your customer or field? Have you tested raw boards and raw parts to see if there are issues with either? do you have x-ray equipment? if back from the field and they had past your tests already I would suspect residues were left on the board. If stright out of your process I would suspect part or board issues. Do ou have solder mask between pads to help prevent shorts in manufacturing process?

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#60810

Solder briding on QFP | 11 January, 2010

If you don't have bridging between pads, how do know that you have a solder short, as compared with some other type of short?

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#60814

Solder briding on QFP | 12 January, 2010

Hello Lyn,

I am experiencing same scenario. There were flux residues on the board. My solder is a no-clean paste. These units fail only when it undergoes 85 deg C and 85 RH. But during room temp, the functionality is OK. Do you have a report that suggest that a flux can conduct at a hight temp and high RH?

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#60815

Solder briding on QFP | 12 January, 2010

To cbart,

The units are from our testing center. Actually I also suspected that it is a board issue. But i dont think its possible for 2 suppliers of board to have same problem. I am also checking the possibility of problem on QFP. Thanks for the share.

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#60818

Solder briding on QFP | 12 January, 2010

I sent you an e-mail with info.

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#60833

Solder briding on QFP | 14 January, 2010

whats the solder finish on the bare boards

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#60914

Solder briding on QFP | 25 January, 2010

so good

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#61073

Solder briding on QFP | 8 February, 2010

Did both board suppliers use the same CAD data to build the boards? We've seen similar where the CAD data was incorrect causing whoever to build the boards incorrectly.

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#61259

Solder briding on QFP | 27 February, 2010

I had a batch of Xilinx chips that I believe had microscopic hairs of the lead frame left as slivers on the leads. These maybe got encapsulated by the solder plating, and then were free to move when the chips were reflowed. You could see the tiny hairs under a microscope. This was only on one particular batch of one type of chip. But, on that board assembly run, it was ALWAYS that particular chip where the shorts were. They were REALLY hard to see in many cases.

Jon

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#61260

Solder briding on QFP | 27 February, 2010

any evidence of dendritic growth?? (cause of the presence of condensed water due to high humidity level)

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#61277

Solder briding on QFP | 1 March, 2010

Pure tin finish? Tin whiskers?

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#61296

Solder briding on QFP | 4 March, 2010

Plz tell me Stencil Thickness ? Solder Paste ? Mesh Size ? Partcle size/type? Viscosity?

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#61327

Solder briding on QFP | 9 March, 2010

Graceyt,

I know you are being shot a lot of info. Have you gotten any resolution to this problem? I've seen similar problems in our thermal chamber with Demodulation units. The IC, in the module, inside the radio inside the chamber at the top of our hot cycle was exceeding its maximum operating temperature. We found this by connecting our temperature profiling mole thermocoupler directly to the IC to see what its actual operating temperature was reaching. It was causing sparatic demodulation errors and took quite a while to find. Hope this helps.

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#61552

Solder briding on QFP | 4 April, 2010

On the Xilinx chips, I am pretty sure these hairs are NOT tin whiskers. The solder in this particular build was SnPb, and pure tin would almost certainly melt at soldering iron temperatures. My theory is that slivers of the lead frame material, likely copper with some plating, is being left after the lead frame is punched out, and is encapsulated in the solder plating. When I reflow the part on the board, these slivers are released and move around. But, that is just a theory.

Anyway, these slivers can be seen within days of the reflow process, when we rework the boards to search for bridges, etc.

Jon

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