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Pin-in-Paste, Intrusive Reflow, Solder Preforms, etc.

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#45916

Pin-in-Paste, Intrusive Reflow, Solder Preforms, etc. | 4 December, 2006

SMTNetters,

I have a product coming down the pipeline that we'd like to make pure double sided reflow, it'll be RoHS product, and the hope is... we'll be able to solder the thru-hole stuff by screen printing solder paste and reflow soldering.

Anybody out there doing PIP/Intrusive reflow with Lead-Free? If so, what are the key variables to look for? Pad design, I know, is important, but what about Stencil Design? Can one overcome a poor pad design on through-hole by doing intelligent stencil design?

The beef most people had against PIP has been the lack of top-side wetting, and the appearance of sunken solder joints. Has anybody tried solder preforms to help with this?

I hope to get responses from you folks. :) It seems most of my inquiries on this forum are unanswered. thanks in advanced.

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RDR

#45919

Pin-in-Paste, Intrusive Reflow, Solder Preforms, etc. | 4 December, 2006

Made no changes to pip process for lead free. Everything stayed the same. just have to ensure that components can withstand the high reflow temp.

incomplete hole fill is from aperture not being big enough. Many people forget that paste reduces in volume by about 50% after reflow. I use this formula to calc how much paste needs to be applied.

hole volume (hole volume - lead volume)x 2.2. this allows for shrinkage of volume and adds 20% for top and bottom fillet.

Russ

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#45933

Pin-in-Paste, Intrusive Reflow, Solder Preforms, etc. | 4 December, 2006

Solder preforms can be used in SMT assembly for through-hole pin-in-paste process. In this process and modified aperture is used to print the paste with standard stencil printing, then a solder preform is picked and placed by a machine into the solderpaste. Solder preforms come in a variety of shapes, many in tape and reel to load onto a p&p machine.

Please go to this web site link for more information. They have good applications engineering support, so contact them for specific details about this process:

http://www.indium.com/products/solderfabrications/preforms.php

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#46027

Pin-in-Paste, Intrusive Reflow, Solder Preforms, etc. | 6 December, 2006

We would be able to help you in any way that we can. There was an article in SMT magazine that explains a lot. Also, we have data on other processes that have successfully done this conversion.

This has been a popular way of eliminating the conversion of a wave machine to Pb-Free.

Feel free to contact me offline.

Regards,

Mario Scalzo, CSMTPE, Dartmouth 6 Sigma Green Belt mscalzo@indium.com

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#46179

Pin-in-Paste, Intrusive Reflow, Solder Preforms, etc. | 15 December, 2006

Good morning,

The critical points for successful PIP technology are:

1. Gap between THT lead and PHT hole. It shouldn�t be greater that 0.2mm; 2. Lead shape. THT leads MUST be straight or you�ll get excessive voiding otherwise; 3. As Russ said, paste volume. Paste volume being deposited have to be two times more than �gap-wall� volume.

Stencil design is very critical thing to think about. Overprints together with stepped stencils are widely used for PIP. Calculate stencil thickness and make overprint and at least 50um step above your THT. It should work.

BR, Pavel

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