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Solder Paste Printing First Pass



Solder Paste Printing First Pass
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. Phil Zarrow and Jim Hall, the Assembly Brothers, share their own experiences and insight.
Board Talk

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

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.
Mike Burgess, ASM Assemby Systems

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