Metal micro perforation

Question

I'm trying to design a metal surface with micro-perforation for a product and light it from other side with LED, such that the perforated pattern appears only when lit.

In my previous prototype, which used laser drilling (20 micron holes) for perforation, there was considerable warping of the metal film (around 0.3 mm thick) which rendered the prototype unusable (aesthetically)

Another problem I had with the prototype was that the light was not getting through perforation evenly i.e., I was not able to see the light from different angles.

On initial research about laser micro-drilling I found that the thermal conductivity of material plays important role in heat affected zone, which could result in warping. The material used for prototype was stainless steel, which has comparably lower thermal conductivity than aluminium.

• What care needs to be taken to avoid or reduce the HAZ and hence the warping?
• For the visibility of light through perforation, will the hole size and spacing directly affect this?

I am trying to achieve the appearance like shown below

Misfit Shine fitness band; the micro-perforation on dial is invisible when unlit.

Answer 1

If you can use metalization to create your film, you could create a mask in the required pattern and just coat on top of it.

However I assume you only have a laser at your disposal. Your heat affected zone will depend on the speed at which you remove material. Higher power will tend to drill through faster and affect a smaller area but it may create more warping as you create a steeper heat gradient. There are two things I can think of trying that worked in other applications:

1. use a backing that will spread the heat (aluminum/copper), it may reduce the amount of stress in the material
2. try using different settings (power, travel speed) to reduce the stress in the material. Document your trials and see what works best. (Sorry I can't help further on what settings to use, my application/material was a bit different)

Answer 2

What about using a sintered metal? Powdered metals can be mixed and an acid might be able to remove one metal in specific spots allowing the light to shine through.