Unexpected Issues in Excimer Laser Micromachining- Examples
Example 1
You approach a service provider for a project involving machining 80 micron holes through 300 micron thick glass plates. The provider comes back with excellent sample cuts using a 193 nm excimer.
You place an order for 20 plates, each with 250 holes. The first batch comes in, you check the holes sizes and find a pattern of hole sizes shrinking- until they go out of spec 3/4ths of the way. You drop the vendor after you find the second batch defective, believing it to be bait with sample and switch in production tactic.
The Truth
The laser used for the cutting was a high powered one. Unfortunately, it also heated up after continuous firing, and the cavity mirrors moved around slightly, causing the sweet spot of the beam to drift in and out of the imaging aperture. The holes varied in size- those drilled later in the sequence kept getting worse. The laser energy was measured for the whole beam using a 4% reflecting mirror right in front of the exit aperture of the laser- and that of course remained constant. The problem was with the beam ‘walking’ around.
Example 2
You inherit a project, one part of which involves the microfabrication of 200 micron wide washers out of PLLA. It was an exotic material several years back, and your predecessor paid a lot for the parts because other providers did not understand the material and hence no-bid.
On one of your visits to a conference on biodegradable polymers, you mention the laser cutting of washers. Comparing notes, you find that you have been paying 10 times the going rate. You are pretty upset about this, and drop the vendor without discussing it with the vendor, and refuse to even return their calls.
The Truth
PLLA is no more an exotic material. The average energy had to be carefully controlled to prevent melt, and the smarter providers started using high frequency quadrupled YAGs bringing down costs to the level of other polymer-micromachining. Unfortunately, your provider didn’t keep abreast, and was happy since there was a steady stream of income. Still using a good old excimer at 100 Hz, and just an average profitability.
Suggestion
Occasionally, just once in a while, talk to people who know these things. Like me 