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Solder Paste Volume

Juergen

#5783

Solder Paste Volume | 29 March, 2001

Hello everybody,

Two questions came up during an audit (old topics once more):

1. we are not checking the solder paste volume/pad height after printing - others are using an AOI, but is it really necessary? We just do visual inspection randomly. We don't have problems based on too much or few solder tin.

2. we should maintain our stencils by measuring their tension. Does it help to improve the printing quality?

Can somebody give some hints?

Thanx

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Peterson

#5784

Solder Paste Volume | 29 March, 2001

AOI technology is over-priced and inconsistent...lots of false errors. Your best bet is a paste height measuring device (3-D) Cyberscope makes one for 25-30 thousand. This process is really only necessary for high volume operations. As for you question about stencils: Keeping stencils clean is all that is usually necessary to ensure good print quality...provided you do not damage stencil aperatures..metal cleaning tools should NOT be used. A sonic cleaner or alcohol/wipes will usually clean adequately.

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JohnW

#5797

Solder Paste Volume | 29 March, 2001

measuring Paste volume or at least paste height is an essencial part of any SMT process. You've got to control those input's.... Paste volume determines how much solder is available for your joint so theres a direct to joint reliability / PCB reliability. If you don't know how much paste your putting down how do you know that you've got enough? for instance when your looking at the lead's on your QFP's are you getting both a heal and toe fillet?, are you getting the paste wettin gout over the pad? this is really one of those fundimental's that you need to do. And you don't have to spend a fortune to do it, there's no need to rush off and buy an in line cyber or such if your process doesn't need it, many people manyfacture off line system's that you can use, you don't need to measure every PCB to keep your process in control, a few every couple of hours is fine or evey hour if your running fine pitch.

JohnW

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JohnW

#5798

Solder Paste Volume | 29 March, 2001

measuring Paste volume or at least paste height is an essencial part of any SMT process. You've got to control those input's.... Paste volume determines how much solder is available for your joint so theres a direct to joint reliability / PCB reliability. If you don't know how much paste your putting down how do you know that you've got enough? for instance when your looking at the lead's on your QFP's are you getting both a heal and toe fillet?, are you getting the paste wettin gout over the pad? this is really one of those fundimental's that you need to do. And you don't have to spend a fortune to do it, there's no need to rush off and buy an in line cyber or such if your process doesn't need it, many people manyfacture off line system's that you can use, you don't need to measure every PCB to keep your process in control, a few every couple of hours is fine or evey hour if your running fine pitch.

Interm's of your stencil, I agree that cleaning them properly is all you should really need, sure when your finished the run it's good to check the tension, but that can be a visual. I know most people would say you can check it befor or during your set up but for me if you leave it till then it's too late, after all if you do need a new stencil you've set a line up for no reason and wasted a hell of a lot of valuable time, money and resource...but taht's just me

JohnW

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Steve Brown

#5891

Solder Paste Volume | 6 April, 2001

You can buy plenty of paste height measuring systems today, ranging from full 3D laser systems to systems using an oblique light line which will measure the paste height only. I found that the lowest cost option was to attach a DTI to the focus control on a microscope. Focus on the board, zero the DTI, then focus on the highest point on the paste. Complete this operation on the 4 corner of the board and in the middle, and on any critical components such as fine pitch / BGA's and you have a picture of paste height across the board. To take this one step further, try using a design of experiments program to determine which variable in the printing process (print speed, pressure, separation speed, support) has the greatest effect on the paste measurement, then measure this variable on a regular basis, this way you capture potential problems before they happen. Beats having to clean down boards which can cause solder balls when re-processed.

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CAL

#5894

Solder Paste Volume | 6 April, 2001

FYI- Toe Fillets have not been required per IPC 610b/c (they are nice to have though). Remember before Solder paste inspection equipment The Solder powder type/size, stencil type, and apertures are what defined volume. The need has not been until recently to use solder paste inspection units - due to smaller/ finer pitch components. Where processes go arye (we ain't talking bread) is when the wrong paste (powder size) is used and lack-o-cleaning. If the apertures get clogged this affects the amount of solder paste deposited.

Also, you can contact me or down load our Feb empfasis technical news letter from our website. It has an article regarding Stencils. http://www.empf.org

CAL

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sinclair

#5897

Solder Paste Volume | 9 April, 2001

Why measure solder volume? I believe if one understand the process well enough, the effort should be spent on area that will gives better indication of your solder printing process. From my personal experience, a lot of auditor knows little of the process and just merely follow some instruction written on the audit sheet that this needs to be done - its the "norm", passed down from older generation. Gone were the days of rubber squeegee and low tech printers. Its time to move on to verify on areas on the printing process that will gives a better indication of process control. For example, verify that the squeegee makes a clean sweep on the stencil or check for blockage/paste release on the whole stencil.

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#5900

Solder Paste Volume | 9 April, 2001

I've been wondering if I was the only person thinking this. There are so many print parameters that are programmable now on new machines (squeegee pressure, height, speed, snap-off settings, cleaning intervals) that the process would (in my oh-so-humble opinion) be better controlled by verifying stencil cleanliness, tension, etc.

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#5905

Solder Paste Volume | 9 April, 2001

First, some people wait a lifetime for ... ;-)

Second, how do you guys measure the stencil aperture clog? What do you think of the Magnaplancil from Fendelaz? It�s a double fyv-blue-green CO2 laser refract-defractometer. ;-)

Third, do you really find that the only variable that affects print volume is stencil issues [eg, clogging of apertures, stencil maintenance, etc]? In the old days, there was some 34 factors that affected print quality.

Fourth, isn�t the amount of fresh paste on the pad when the board moves to placement that�s the important issue?

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#5912

Solder Paste Volume | 10 April, 2001

Didn't you hear? Fendelaz went out of business and sold the rights to the Magnaplancil to Amahlmahay.

Sure, all the standard variables still affect the print quality (aka registration and volume) but if the machine controls everything but paste dispensing and stencil quality AND does 2D print inspection of both the stencil and the print, don't you think the time could be better spent doing something besides measuring paste height?

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#5915

Solder Paste Volume | 10 April, 2001

What time? An in-line bot with a vision system tuned for paste recognition can measure a different portion of each board and keep pace with the placement machine all day long.

I don't understand what you guys propose as an alternative. Realistically, I'm not so sure that the Magnaplancil isn't just some vaporware thing. [There, I said it. I hope you guys are hanging you hats on that machine!!!]

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#5916

Solder Paste Volume | 10 April, 2001

OK, you're talking about inline AOI doin' all the work for you, for a price. Fair enough.

If you can't afford the inline post-print inspection equipment, though, I still think you can depend on the 2D inspection of the paste to tell you if you've got a good print. I just don't see the paste height varying enough to mandate another inspection.

Besides, why did I pay $20k for the 2 1/2D inspection software option on my printers if I still need 3D inspection? C'mon, Dave, cut me some slack. ;)

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#5917

Solder Paste Volume | 10 April, 2001

Listen, there is a $20 to 30k laseriffic paste measuring system that is not only very expensive and a major bottle neck, but its limited accuracy is the kicker that makes this little item a really special!!! [What a combination, eh???] And that doesn't even touch on the calibration costs of the fine machine.

Do a gauge R&R on your fine laseriffic machine and you'll be scratching your head even more than you are now.

I think you should be making in-process measurements of things that are important. [NEMI recommends: (1) Measuring solder paste shape, height, volume, area, registration, & paste br�dging (2) Inspecting/controling solder paste deposits for fine pitch & 0402s] I think even though you have a tool for making a measurement that capability does not necessarily ordain the tool as the one you should be using. [We have a rulers, but don't use them for quality measurements.]

I think the tools used for making in-process measurements should meet the quality system requirements for accuracy. I think the tools used for in-process measurements should be straight forward, relatively simple, and unambiguous to operate correctly.

I think the costs of making the measurements should be less than the benefits of making the measurements. [Ami done, eremi looping??]

If you are not getting good process measurements and tightening your control with your $20k laseriffic machine [and asking the questions that you're asking], then maybe the rep for that machine can come into your plant and explain why you spent so much money on such a very nice boat anchor [cough, cough er, machine].

A microscope like the one mentioned by an earlier poster on this thread has a much better gauge and costs far less than the laseriffic machine.

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#5926

Solder Paste Volume | 11 April, 2001

I think we've miscommunicated....I don't use that thing for measuring paste height or volume as part of the process because it's not repeatable from one operator to the next. I use it more to measure radial tape and reel parts against EIA-486, actually.

My point was that since my printer inspects pre-selected areas for stencil clogging, paste deposit area, registration, bridging, and does have sensitivity to the shape of the top of the deposit (it will reject an odd form top surface as long as it wasn't taught to accept it initially), I've decided NOT to measure paste height with my non-repeatable (and actually $15K I think) paste height measuring thingy.

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Cyber Legacy Division

#5928

Solder Paste Volume | 11 April, 2001

Let me put my two cents into this argument..After being part of many extensive studies conducted to determine the benefits of solder paste inspection, there has never been a case where the customer concluded that paste inspection (Height or Volume)was an unnecessary process control tool. In Fact, consider the methods in place at the largest OEM's and Contract Manufacturers throughout the World and you will find that solder paste inspection is a key factor to yield improvement strategies. By relying on 2D (Area) inspection to provide all the answers to your printing process, you leave yourself wide open to a number of variables 2D inspection will not catch. By implementing volumetric solder paste inspection, you will not only achieve valuable 2D information, but also more comprehensive information related to the overall structure of the solder paste deposit(Average Height, Max Height, Min Height, True Volume). In addition, the old saying that "a picture is worth a thousand words", holds true for paste inspection systems capable of providing true 3D volumetric data. Now, instead of relying on raw and rather unattractive data to tell you the answers, 3D color profiles of the solder paste deposit can be displayed. From these profiles, an operator can analyze failed solder paste deposits and come to a more realistic corrective action based upon what these see.

As far as the low cost(Cross Section - Height Only or Focusing Microscopes)inspection system are concerned, they perform as they were intended. These systems are for quick sample measurements to initially setup the screen printer. They are very slow and can be fairly unreliable when multiple operators are involved. On the other hand, they are an ecomical alternative to high priced in-line systems.

The best advise I can give is to evauate your printing process to determine if yield improvements could help your bottom line. My quess is that everyone small and large could benefit from a closely monitored paste inspection strategy.

Thanks

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