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Is it recommended to print one cycle before printing the first production board? I could use a scrap board or blank plastic card for the first print. Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
With over 50 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis.
He has vast experience in SMT equipment, materials and processes.
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics.
He is a pioneer in the science of reflow.
Transcript
Phil
Welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting. The Assembly Brothers, Pick and Place.
And if you can figure out which one is Pick and which one is Place, more power to you. But that is not really what matters today.
What really matters is this question we received today. This is from S.G. He writes, "Is it recommended to print one cycle before printing the first production board? I could use a scrap board or blank plastic card for the first print."
Jim
Yes. This is an issue to the wonderful world of setup. Of starting up a line to produce a different product than you have been producing or the first product in the morning. The idea of being efficient and minimizing time, materials and everything.
So yes, of course you could print on a scrap board or a blank plastic card but how are you going to evaluate it? What is the issue here? I want to make sure that my printer is ready.
The question you could ask yourself is, why wouldn't it be ready if I properly put on the solder paste and kneaded it if I have to. Why shouldn't my first print be good?
If you say well, I really need to be sure then how are you going to determine it? If you use a scrap board that would have fiducials then you could evaluate it using an automatic solder paste inspection, either the 2D on your machine or a 3D after the machine SPI system.
If you use a blank plastic card the only way you can inspect that would be visually. That is not a really good technique for evaluating the quality of printing.
But in any case, suppose you print on a scrap board or blank piece of card and the print is good. What do you do?
Well then you put a real board in and print it. So you have wasted that first print, and the time it took you to print it.
Whereas if you print it on a good board and it looked good you can immediately start your production with your first board going into your first placement machine. Obviously if it wasn't good you would have to clean or correct that first board.
So those are your options. I would use the first board and try to get your setup procedure so that your first print is good. You have good solder paste at the proper temperature.
It is properly applied on the stencil. You have kneaded the paste with your squeegee if that is an option on your stencil. So that your first print is good.
You inspect it and then you immediately put that board in your placement machine and you are up and running. You have reduced your overall setup time. Got your line up running faster and increased your utilization and your productivity.
Phil
It is almost a matter of how much faith do you have in your initial design and experiment when you arrived at the initial settings on the printer. How much faith do you have in the maintenance of the printer for consistency?
And the fact that your operator follows proper setup procedure. Then it becomes, as Jim said, an efficiency situation, best practices meet efficiency. Do you think that is the best way of putting it?
Jim
Yes. And the main question is, why wouldn't that first print be good?
And what can I do to make sure that it is good so that I can immediately start my production and not waste any more downtime.
Phil
Very good. Well we hope that we answered your question as well as whatever other people are pondering these days.
Just to remind you that, although the IPC tries to come up with a new acronym every time we say it, you have been listening to Board Talk with Phil and Jim. And whatever you do, however you are applying your solder paste please don't solder like my brother.
Jim
And don't solder like my brother.
Comments
The focus here is what to do about checking the quality of the first print? My question is what to do about the second print? There are two strokes and every manufacturer has issues with stroke dependent offsets, it's just a matter of how much. From measurement and experience, brand new calibrated printers often exhibit up to 80um (3.1mil) offsets in at least one stroke direction. Most manufacturers are specifying at least 20um wet print accuracy these days.
Checking print quality is one thing, adjusting accuracy in X, Y AND THETA during setup is quite another when starting a new production run. It's slow and prone to error. BOTH strokes need to be accurate! If you don't measure, you don't know. And, when you don't know, quality can suffer!
Michael Sivigny, CeTaQ Americas
Several questions you may also to considers *Can parts be soldered free of defects when the solder volume changed? *Is the stencil used in the first time and what is the quality of the stencil? *Is there any residue or dust after we clean the stencil? My team did a lot of small volumes or prototype only jobs which introduce a lot of new, unofficial released, limited quantity parts. To minimize the rework and discover the possible quality issue before production, these are some of questions we asked first.
Beside the preparation and inspection on the stencil when we received it, any material added between stencil and board may cause some degrees of side effects. Depends on the purpose, my team may just cover one layer of 1 mil thick Kapton tapes or covered just a piece of paper in the first cycle if there is no solder sample provided or just simply printed on solder samples. And, you may need to clean the bottom side stencil after the first print.
Fred Huang, Sparqtron Corp.
The viscosity of paste reaches optimum during a few kneed strokes and this procedure should be followed for all but the easiest to print (Area ratio above 0.7) boards. During these kneed strokes if you look closely you can actually see the paste rolling and texture improving. Unfortunately as mentioned sometimes a kneaded board is not suitable for production and knead cycles take time and must wait for production to restart after idle time (Restart and immediately delay production due to Knead)
Interestingly during the development of a printer I was working on, I proved that a few 30mm flood print cycles on the support rail area of the printer are sufficient to work the paste, which can be done with no PCB present and therefore not halting production or potentially producing a badly printed (Kneaded) PCB. But so far no print manufacturer has taken up this methodology!
Robert Gray
Visit my directory page to see a video that will show you show how to do test prints on test boards dedicated for first prints or using a film overlay. http://www.circuitinsight.com/directory/51316.html
Bob Willis, Bobwillis.co.uk
Several knead strokes are critical in preparing solder paste for a first print or after a long pause between prints. It's a cheap and easy insurance policy.
Timothy ONeill, AIM
Polymer Plastics offers their low tac Trans-Mask clear overlayment in roll form to allow you to adjust your stencil and see the alignments.
Larry Stock, Polymer Plastics Corp
Most PCB suppliers will give you X-outs or test scrap boards that can be used for setup so you don't waste good boards validating your stencil operation. I think it's an absolute must to make sure you are printing properly and the registration is correct, especially with BGA's. There are too many variables that can go wrong, from the stencil being plugged, misaligned or the squeegie being worn out or the pressure or angle set wrong. Things wear out.
Bradley Fern, Entrust Datacard
We use 3M #336 transparent film, leaves no residue, not only is it good for checking your first print, it's also good for checking your new stencil against the board to verify the stencil has no missing or extra apertures, even the best stencil house can have issues or you may have been provided with the wrong stencil file.
J. Dowsey, Sanmina
The reason the first print might not be good is that the paste has not reached equilibrium across the stencil and blades on the first stroke. Keeping in mind that most shops apply paste manually to the stencil with a knife or caulk gun you can get air bubbles or uneven deposits. These can cause skips and uneven aperture fill. Once the paste has rolled across the stencil this should clear up. Automatic machines will have a knead setting to do a repeat stroke on the first print or after a specified idle time to account for the setup or paste slumping over wait time.
Don Adams, Bose Corp.
Beans International offers a low adhesive, ESD safe, transparent material for preforming kneading and paste alignment test prints at the screen printer.
