Phil
And welcome to Board Talk. We're the Assembly Brothers, Jim Hall and Phil Zarrow, of ITM Consulting, and we're here to answer your questions in SMT process, equipment, materials, procedures, and lots of other stuff.

Jim, what's our question today?

Jim
Measuring component height after reflow, or what we might call "standoff." This is from CS in Santa Ana, California. CS writes, "I have an SMT component that has a height of eight millimeters, a stencil thickness of 0.5 millimeters. We are using a lead-free paste. The pad size is 11" by .054" The question, is there a method of determining the overall height of the component on the board after reflow.

I have to believe that the pad dimensions of 11" by .054" is incorrect. I would have to guess if that's supposed to be .011" .110". It's probably .110"

Phil, how would you answer CS?

Phil
Well, the question, is there a method for determining the overall height of the component on the board after reflow, the answer is yes.

But from the information he gave us here, that one dimension was accurate or not, you don't really give us enough ______ information. What do we need to know to do that, Jim?

Jim
Well, I don't know that I could it anyway. This is a multi-parameter mission. You've done some of the ideas, the component, the thickness. You've given us the thickness of the stencil. The stencil, 0.5 millimeters, that would be a 20 mil thick stencil.

Phil
Holy guacamole.

Jim
Wow.

Phil
What are we soldering here? That's a question I got for CS. What the hell are you soldering?

Jim
That's a hefty dimension on that. I didn't even pick that up when I read the question the first time.

Phil
Transmission blocks or something? What the heck is this? Wow.

Jim
Yeah.

Phil
But anyway.

Jim
Stencils are usually four to eight mils thick, not a 20 mils thick.

Phil
But let's talk about what are the parameters if anybody wanted to go – yeah. What are the parameters we're looking for in terms –?

Jim
He's given us some of it. He's given us the pad size, the thickness of the stencil, assuming we know what that is. We'd have to know what the aperture is relative to the size of the pad. But most importantly, he doesn't tell us what type of component it is.

Phil
Yeah.

Jim
Is this a QFP? Is this a chip? Is this a BGA?

Phil
Is it a cylinder head?

Jim
So you would need all those things. Even then, you also want to know the weight of the component. But even then, doing an exact calculation is pretty difficult. Most people, I believe, who are interested in this data will actually do some physical measurements for their system. If you're using it to predict the thickness of a stencil, again, you'd probably want to go on some correlation. ‘Cause whatever analysis technique you came up with to predict is you'd want to verify it with a final test result anyway.

Phil
Yeah.

Jim
Also, I want to point out that he's talking the height of the component typically we talk about that in terms of standoff. That is the distance between the board and the bottom surface of the component. Of course, we could just add that to this eight millimeters thick component. But does that height include the leads if this is a lead or BGA?

Phil
Yeah.

Jim
So there'd really be more information needed. Those would be the parameters that you would have to. But in my experience, most people measure this for specific styles of components and then they can estimate it.

Phil
All right. Well, there you go. That's a full baked answer to a half baked question. That's it for this session of Board Talk. You just spent five minutes of your time listening to Jim and Phil. It's something to answer a question.

Jim
Or not answer a question.

Phil
Or not answer a question because it wasn't a question to be answered.

Jim
Sorry, CS, if you were looking for a formula you didn't get it.

Phil
Yeah. So get your act together. Anyway, everybody else, do send in your questions, hopefully, with lots of pertinent data, comments or whatever.

Jim
If you're gonna include dimensions, please check to make sure they're right ‘cause it's kind of hard for us to guess.

Phil
Somebody's missing a decimal point. But anyway, but you can send in this questions, comments, whatever, by clicking on the little comments/questions space on the page there. Thank you for listening to Board Talk. We look forward to you joining us again in future Board Talks where we will attempt to answer questions. This has been Board Talk with Jim and Phil, the Assembly Brothers. And remember, whatever you do –

Jim
Don't solder like my brother.

Phil
And don't solder like my brother and watch those decimal points.

Jim
And keep the kids away from the flux spot.