Phil
Welcome to Board Talk. We are the Assembly Brothers, Phil Zarrow and Jim Hall. Pick and Place or Place and Pick, depending on what angle you’re viewing us at. And today we’re speaking to you from the technical archives of ITM, which most other places pass as a dumpster

Today's question is from a Mr. SC and he asks – he’s got a three-part question. Wow, he’s gonna get a lot of information here. The first question is, "Is there a recommended or a standard usage rate for stencils?"

The second question is, "Should I expect different usage rates for metal, rubber, or plastic?" I assume he’s referring to squeegees, cause I haven’t seen any rubber stencils lately.

And the last question is, "Is there a specific way to determine when it’s time to replace a squeegee?"

All right, let’s do these in order. First of all, as far as recommended or standard usage rate for a stencil, the answer is no, because there are just so many variables. Certainly what the

shape of the stencils, how many apertures there are, as well as some of the inputs from your printer itself, such as squeegee pressure and some of the variables there.

Jim
Most important, squeegee pressure and how thick the stencil is. A thicker stencil is gonna last a lot longer than a thinner stencil.

But I think what you said in design, sharp edges, cut outs, and so forth, there are a number of things you can do in design of stencils to extend their life, but certainly not having excessive squeegee pressure is probably the most significant in increasing the life of your stencil. And handling. I mean handling these things. When you take them on and off, they’re stretched in that web in your stencil and if you’re not careful with them, you bang them, you scratch them just by handling.

Phil
That’s right. It’s not hard to ding one. Usually the answer to that question is the stencil pattern will be obsolete long before the stencil itself is worn out.

Jim
I think that’s typically right, unless you’re in a very high-volume product it’s much more common to lose a stencil because of mishandling.

Phil
And even then, we don’t really have any numbers. I know there’s some instances where I’ve experienced a quarter of a million prints from a given stencil.

Jim
In other words, put it back, when you’re probably talking about a 6 or 7-mil stencil, right?

Phil
That’s right. That’s true, too, yep.

Jim
Okay. The difference in usage rates with a metal, rubber, or plastic squeegee. If you are using a rubber squeegee, you probably can expect a longer life on pure cyclical use, but to be real honest, we don’t find a lot of people using rubber squeegees and certainly not for high volume.

Phil
Yeah, and a number of reasons. I mean one of the reasons we moved away from rubber in the first place, besides the wear factor, was the fact that you need a different hardness or durometer for depending upon the pitch that you’re printing. In most boards today, we have a wide range of print, so metal was a one-size fits all as far as pitch goes and the metal itself is pretty long lasting. Again, unless you drop it, in which case time for a new one.

Jim
But it leads us into the third question, "Is there a specific way to determine if it’s time to replace a squeegee?" And that was the problem with rubber. When did it need to be replaced? When was it getting a little worn or out of there? That was very difficult. Much more clear cut with a stainless steel squeegee where unless it goes out of flat or unless it

gets dinged, it’s probably okay. So it’s much easier to see defects and wear that’s significant to cause you to replace a stainless steel squeegee.

Phil
Right. On top of that, there’s also a few aftermarket squeegees that are available that are the metal, of course, that have various treatments on them that supposedly also, per the manufacturers, extend the life of the squeegee in terms of number of print cycles by quite a large percentage, according to their claims. But again, a lot of it has to do with setting everything else up right and have good proper care and treatment.

Jim
Right, and with squeegees and with stencils, most of them have to be replaced because of mishandling, not because you ran too many prints, good quality, well-adjusted prints on them. And so if your’re having a concern, questions like this, say, "Hm, I think this person probably had some questions about some need to replace these." and I would certainly look at your handling and your set up procedures because that’s much more likely the cause of early replacement.

All right. Well, you’ve wasted another five or six minutes of your valuable time listening to us drone on about our knowledge of printing and all the other various sundry aspects of electronic assembly.

Phil
But we did answer all three questions so you’ve got to credit us that.

Jim
We did. You got your money’s worth.