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0402 bridging

Views: 1931

ldempsey

#74021

0402 bridging | 2 June, 2015

Hello all,

Some background. We have JUKI machines (FX2, KE2000's and KE3000's)

We're looking into an issue with 0402's in close proximity to each other. The paste gets mashed into the paste from adjacent parts. Some have suggested I deviate from JUKI's default place stroke of 0.5mm to 0.0mm. I've known this to cause problems elsewhere.

Does anyone else have any ideas? Should this issue be tackled at the PCB design level or the stencil edit level?

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#74022

0402 bridging | 2 June, 2015

What is the reduction in aperture size for your stencil versus pad? Or are they at 100%?

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#74023

0402 bridging | 2 June, 2015

Well, I'm speaking in general

Our stencil guy insists on those part edits at 100% He's one of the loudest voices calling for me to "Stop slamming the parts into the PCB"

All my research so far says we need to be looking at the stencil apertures.

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#74024

0402 bridging | 2 June, 2015

Les,

Some of the answers to design or stencil aperture/placement machine depend upon what is the current spacing between your components which you didn't specify. Chip components such as 0402's and 0201's typically have very small reductions in paste aperture size. Chip caps/resistors should typically be spaced .020" from each other, +/- .005". having said that I have had some as close as .005" on some very tight designs and not bridged. On 0402s(inch) we typically reduce 2 mils on each side. If the paste from two parts is squeezing out far enough to touch I would guess that you either have too much placement force or the machine doesn't realize the correct board height and is pushing the parts down too far. Hope this helps.

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#74028

0402 bridging | 3 June, 2015

Well, it took me a while but I had a look at some gerbers.

On a PCB with neighboring 0402's 0.006" apart, and paste reduced 0.75mil on each side, I get lots of bridging.

On a later rev of the same PCB, we have neighboring 0402's 0.018" apart,and paste reduced 0.2mil on each side and no problems at all with a place stroke of 0.5mm.

We were able to alleviate some of the bridging by reducing the place stroke, so the part just barely touches the top of the paste, but it ended up causing problems for the machines releasing the parts.

I'm hoping to avoid reducing any place strokes on 0402's/0603's/0805's at all, since these changes will end up being global. I don't think JUKI is about to stand up and say "Yeah, 0.5mm default place stroke is a design flaw." (Although in one manual I see they say 0.2mm is the default for 0402's and 0603's, yet the Database and Machines still default to 0.5mm)

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