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PCB related question

Hi everyone,
Here's the dilemma. We want to ensure accurate positioning of a SMT
connector.

We can specify better accuracy on the drilling of the pcb (for
alignment pins) and place fiducials on the board for AOI pick and
place.

However, we want a visual feedback after assembly.

I've proposed putting a pattern on the foil with 1 mil steps and a
reference mark.

A kind of vernier if you will. I'll be putting a big shape so it's
easily manufactured, but how well will 1 mil steps come out?

Anyone every tried this? Does this have a name?

And yes, I will be calling our PCB shop.
 
C

Christopher Ott

Jan 1, 1970
0
Hi everyone,
Here's the dilemma. We want to ensure accurate positioning of a SMT
connector.

We can specify better accuracy on the drilling of the pcb (for
alignment pins) and place fiducials on the board for AOI pick and
place.

However, we want a visual feedback after assembly.

I've proposed putting a pattern on the foil with 1 mil steps and a
reference mark.

A kind of vernier if you will. I'll be putting a big shape so it's
easily manufactured, but how well will 1 mil steps come out?

Anyone every tried this? Does this have a name?

And yes, I will be calling our PCB shop.

You will not be able to get 1 mil traces on your PCB. How small you can go
depends on the board house, and copper thickness, but I would expect no
smaller than 6-8 mils. If you choose this path, you will need to leave some
soldermask off the spot where you want to view the traces.

Does your SMT connector have alignment pins on it? That should take care of
any drifting in reflow...

Chris
 
D

David L. Jones

Jan 1, 1970
0
Hi everyone,
Here's the dilemma. We want to ensure accurate positioning of a SMT
connector.

We can specify better accuracy on the drilling of the pcb (for
alignment pins) and place fiducials on the board for AOI pick and
place.

However, we want a visual feedback after assembly.

I've proposed putting a pattern on the foil with 1 mil steps and a
reference mark.

A kind of vernier if you will. I'll be putting a big shape so it's
easily manufactured, but how well will 1 mil steps come out?

Anyone every tried this? Does this have a name?

And yes, I will be calling our PCB shop.

And they will tell you they can't do 1mil traces. 3-4 mil maybe if you
pay them.

How much positional accuracy do you need on this connector?

If you have physical allignment pins on the connector then I can't see
why you need to even check the allignment after assembly?...

Dave.
 
You will not be able to get 1 mil traces on your PCB. How small you can go

I'm not really asking for 1 mil traces. I'm drawing a solid piece of
copper of about 100x50 mils, but it has steps on it that change by 1
mil. It looks like stairs. I figure that there will be enough of a
difference on average to serve as a visual reference. There are no
features below 10 mils on my copper piece.
depends on the board house, and copper thickness, but I would expect no
smaller than 6-8 mils. If you choose this path, you will need to leave some
soldermask off the spot where you want to view the traces.

Does your SMT connector have alignment pins on it? That should take care of
any drifting in reflow...

It does, and it doesn't. We are having all kinds of problems.
 
C

Christopher Ott

Jan 1, 1970
0
I'm not really asking for 1 mil traces. I'm drawing a solid piece of
copper of about 100x50 mils, but it has steps on it that change by 1
mil. It looks like stairs. I figure that there will be enough of a
difference on average to serve as a visual reference. There are no
features below 10 mils on my copper piece.


This will etch out as a diagonal line. Even if the traces are 10 mil, you
are asking for 1 mil resolution...

It does, and it doesn't. We are having all kinds of problems.


What kind of problems? If there is an alignment locator on the part, and you
have an alignment hole on the board, it seems reasonable that you should get
some decent accuracy. Is the locator hole too large? Are you using too much
paste and floating the parts? What kind of problems specifically?


Chris
 
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