How to align component during assembly

[pastaclub]

How can I make it easy to properly align a component with the front panel in volume production?

I have a flex PCB with a ToF sensor chip and two capacitors. The shape of the flex PCB can be changed if needed. The sensor is 4.4 x 2.4 mm and has two tiny holes on top that need to be aligned with two transparent windows (1.3 mm diameter circles) in an otherwise black glass which also covers a nearby LCD.

My front panel sandwich consists of 3 layers of materials glued on top of each other:
- aluminum plate
- printed acrylic
- cover glass

There is a cutout in the acrylic with the same shape as the flex PCB, so the flex PCB sits between the aluminum plate and the glass. The glass comes already laminated to an LCD which is installed in another cutout.

In an ideal world with zero tolerances, the circular windows in the glass would be perfectly centered over the holes in the sensor... but I need to allow for some tolerance, and I don't have that much room to work with since the circular windows are only 1.3mm in diameter and need to fully cover the holes, so it better should be accurate to +/- 0.3 mm. I wonder if I should just rely on making the cutouts as tight as possible (within manufacturing tolerances) and rely on everything fitting, or if I should leave a bit of room for manual alignment.

Photo of the flex PCB with sensor is attached. Sorry for bad photo quality.

[thm_w]

- Can the acrylic cutout be made to center the sensor itself and then have a larger tolerance for the flex PCB? You'd have to quote from the machinist what spec they can do, but <0.3mm should not be much issue.
- Can the 1.3mm circular glass windows be made larger? I guess not since its premade
- Can you ask assembler what they would be able to do in terms of component tolerance or advice? Maybe 0.1mm or so? Usually the solder itself will center the part fairly well.

You could also test how far out of alignment it can be before performance is affected.