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Solder Paste Height



Solder Paste Height | 5 January, 2001

Hey everyone, Does anyone out there use a solder paste height measuring system ? I would like to know what the standard is for paste height compared to stencil thickness and how you use it as a process tool. I appreciate any help. Thanks, Steve.

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Re: Solder Paste Height | 6 January, 2001

We have talked about using mircoscopes and laser thingies for measuring paste height on SMTnet previously. [Fine SMTnet Archives might give background.] Some people use a 0603 chip cap as a standard.

I'm not sure how stencil height relates. Paste volume is the issue. Some people use paste height as an analog for volume. Check the Archives on this one also.

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Re: Solder Paste Height | 6 January, 2001

On a related note, I'm wondering if any of the newer devices have any way to factor in paste not releasing from the corners, or for that matter, radiused, oval, or round apertures. We have an LSMII, and all it does it let you draw a rectangle around the deposit and assumes that it's filled. You have to let operators adjust the box size to compensate for irregular deposits. Not the most controllable process.

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Re: Solder Paste Height | 6 January, 2001

While solder paste height is one possible process indicator, the other guys are right on the money - volume is key. One way to study overall paste volume is to measure every single pad, using a 3D laser analysis (see you next week for board 2)...

OR: measure the weight and calculate the volume (density of 90%w/w Sn63 paste is about 4.8g/cm3) of paste by simply doing a 'before and after' weighing of the board. This is a lot trickier than it seems, as you need a pretty sensitive scale and some nifty draught-proofing. This is not (as yet, at least) an in-line process!!

I'm doing a paper on this at the moment - probably at IPCWorks later this year.


Hope this helps

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Re: Solder Paste Height | 8 January, 2001

You are 100% correctamundo!!!! Those units are very operator dependent. $15k for a lousey gauge R&R doesn't make me want to stand-up and salute.

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Brian W.


Re: Solder Paste Height | 12 January, 2001

Cyberoptics makes a device called a Cybersentry. wonderful machine. Will work in line or off line. I used one in a former company. You program what pads and locations you want, and it can measure volume or height, and give you charts. You can enter control limits and it will do the charts and give alerts for out of control conditions. Instead of measuring one line across the top of a pad, it scans the entire surface of the top of the pad and calculates the average. That accounts for some stretching from poor release of paste. It takes all the operator error from the measurements. We had one machine and used it off line, but I knew of a company that used them in line. They programmed it to scan different location on successive boards, so that after 5 boards they had monitored the entire board. I believe the new one is Cybersentry 200 or maybe SE300. Web page is


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Re: Solder Paste Height | 23 January, 2001

We have evaluated 4 different AOI machines and the General Scanning 8200 machine was the best. Great G R&R.

As far as paste height goes, it is very paste dependant. I recently completed a DOE comparing laser stencils to EFab, varying 0.5 mm pitched CSP shapes and sizes, etc...

The end result was I got ~75-85% paste release. Paste height should be close to nominal (5 mil if using a 5 mil stencil) in a stable process. But, as someone mentioned, VOLUME is the key variable you should monitor and control.

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