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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

100% solder coverage

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100% solder coverage | 12 September, 2007


We are an electronic assembly contractor and one of our customer requires a 100% solder coverage on pads for their products. We are using flex pcb and we mount only one component (LED for backlight application). The solder paste we are using is Pb-free from Senju (M705-GRN360-K2V). Our oven profile has peak temp. of 245 �C. Our problem is that a little offset in printing results to exposed pad which is unacceptable based on our customer standard. It seems that the paste is not wetting completely or not flowing during its liquidus state to cover the whole pad. Any idea how to solve our problem?

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100% solder coverage | 13 September, 2007

Good morning,

Overprint, i.e. make stencil openings for your LED larger. Add printer accuracy to aperture size so that paste would always cover the pad.

BR, Pavel

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100% solder coverage | 14 September, 2007

That is inherent issue with lead free, you may want to ask your customer to reconsider this specification, It was probably initiated during the pb days when an exposed pad could signify a reflow issue.

Overprinting will give you solderballs and unless you are running wash process this could be an issue as well. I believe however that this may be one of the only options to meet that specification. there is another option called "Sipad" that could remedy this.

Good Luck

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100% solder coverage | 15 September, 2007

Russ Not that we want to give Matt Kehoe an open shot, but are you sure that flex can stand-up to Sipad?

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100% solder coverage | 18 September, 2007

I would have to ask Matt, was just a thought

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100% solder coverage | 18 September, 2007

Simply ask your board manufacturer to Hot Air Solder Level the boards. HASL is a very common procatice at all board houses. Should not add cost and now your board meets this spec before you even touch it.

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