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

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SMT electronics assembly manufacturing forum.

fine pitch QFP



fine pitch QFP | 16 June, 2005

Hi everybody, Can some body tell me that what stencil thicknes is required for the 16mil QFP. I am getting bridging as well as dry at QFP pins. What type of solder 1. Viscocity 2. mesh size 3. flux contents

Should be used for this type of components.

Is any special make is recomended for the same prob.

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fine pitch QFP | 16 June, 2005

The most part I have the most difficulty with is a 16mil QFN. We found that reducing stencil thickness to 4mil, and reducing aperatures for the IC by 20%, and setting local fiducials to the IC helped immensely. We used to get 75% or more bridged out of reflow, I'm down to less than 1%.

We've been using AlphaMetals OM-5000 paste with great results.

This was all done on older machines, too.

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fine pitch QFP | 16 June, 2005

We use a 5 mil for 16mil pitch QFPs, Make sure that the stencil has been polished. Type 3 paste. We have used lead free no-clean, lead no-clean, and water soluble lead pastes for these packages. We set the printer for a slow stroke .7 in/min. with the fastest release speed. I would tell you what it is but our printer just has a percentage (10-100% speed).

We need to wipe the stencil after about 10 prints on average.

If you would like to know what paste we use please E-Mail me offline and I will let you know.

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fine pitch QFP | 16 June, 2005

16 thou pitch parts: Use a 5 thou laser cut electropolished stencil with 0.008"x0.045" apertures and type 3 solder paste.

Bridges Connecting or Partially Connecting Adjacent Leads or Lands * Excessive solder paste * Excessive component placement pressure * Solder paste misplacement * Solder paste integrity * Bent leads * Board vibrations during soldering * Lead plating integrity

What does "dry at QFP pins" mean? Is that "no paste"?

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fine pitch QFP | 18 June, 2005

Thanks to all. I am working on your suggetions will get back as the problem solved

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