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Solder Paste Inspection

Views: 2688

Sundaram

#47107

Solder Paste Inspection | 30 January, 2007

I am a Quality Engineer at a CM in VA. Can some one share their knowledge/ process on how to inspect the PCB after application of the solder paste? Also the major issues / defects that we might experience after the application of solder paste on the PCB.

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#47108

Solder Paste Inspection | 30 January, 2007

The must-do is to inspect for coverage and registration. How much bare pad and registration error you can tolerate is process and product dependant, but you can measure both fairly accurately with a reticle on a microscope.

Developing measurement techniques, calculating coverage and registration error and what-not is part of the fun. Teaching your operators how to do this regularly is the real challenge.

Buying a new inline printer that does it for you is much more gratifying.

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#47113

Solder Paste Inspection | 30 January, 2007

Inspection criteria [B Willis] Solder-paste application * Fine-pitch printing Satisfactory solder-paste should: ** Be aligned with all pads ** Conform to the stencil's pad-aperture size ** Have a smooth, flat void-free surface Acceptable solder paste covers greater than 50 percent of the pad surface. Unacceptable ** Less than 50 percent of the pad surface is covered. ** Solder paste has slumped between the pads. * Chip print deposit Satisfactory solder-paste should: ** Be aligned with all pads ** Conform to the stencil's pad-aperture size ** Have a smooth, flat void-free surface Acceptable solder paste covers <75 percent of the pad surface. Unacceptable ** Less than 75 percent of the pad surface is covered. ** Solder paste has slumped between the pads.

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GS

#47131

Solder Paste Inspection | 31 January, 2007

Hi, as for IPC-7095, in case of BGA, other important value to inspect/measure (3D) is the volume of paste deposit, mainly when mounting Ceramic BGAs.

Regards...GS

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Sundaram

#47161

Solder Paste Inspection | 1 February, 2007

Thanks for your input. Where do I get information about fiducial dimension? Also is there any IPC standard for SMT process?

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#47165

Solder Paste Inspection | 2 February, 2007

SJ

#47573

Solder Paste Inspection | 12 February, 2007

There are several ways to inspect solder paste after deposition. Defects will range - too much paste, not enough, misaligned, bridged, smeared, etc. Some sceen printers have 2D inspection imbedded, otherwise a standalone system for paste inspection can be done after the board leaves the printer. 3D automated solder paste inspection systems will provide the most coverage and typically can keep up with line-rates these days. Depending on what you are inspecting (i.e. the beginning of this echain talks about CCGAs which require volume or 3D inspection) you could consider 2D as well. Just do a web search for "solder paste inspection" and you will find a ton of papers, systems, etc.

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#47885

Solder Paste Inspection | 21 February, 2007

I talked to our quality director and he says every solder joint had to be 50% of the way up on all the parts to be consisdered good.

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oldsmtdude

#48112

Solder Paste Inspection | 2 March, 2007

Agilent SP50 rocks for continuous improvement and pass-fail efforts. You'll see variation you never imagined you had prior.

But be aware you absolutely have to monitor data and tweak your processes to improve results. Do not jump in and try and use it as a pass fail until you stabilize your results.

You may go through oodles of stencils searching for the best aperture design / aspect ratio. And, no the current often used designs rarely work best. Nor does adding extra stencil thickness just for good measure - you'll normally see more stable results with better aspect ratio even if that means overprinting pads when volume is needed.

When you get registration variation consistently down less than +/- 12 microns let me know. ;-)

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Solder Paste Inspection