The ESI Solution: High-Throughput Roll-to-Roll UV Laser Drilling of Thin, Flex Materials

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ESI’s Flex Product Manager, Patrick Riechel, carved out a little time to chat with me at the recent CPCA event last month in Shanghai. Among the topics covered: How ESI addresses issues associated with machining roll-to-roll flex circuits, laser technology, and more.

Pete Starkey: Patrick, it's great to be here in Shanghai at the CPCA show. We're at the booth of WKK, your sales representative in China, and you've explained to me that China is a large and diverse market for you. Specifically, you have been addressing some of the problems of machining roll-to-roll flex circuits. Could you describe some of the realities of handling and machining these materials? What are the problems? How do you address them, and what you can offer with an ESI laser system?

Patrick Riechel: We actually pioneered UV laser drilling for roll-to-roll material back in the ‘90s, together with our partner Northfield Automation Systems, who worked with us on our 5000 laser platform. So UV laser drilling with roll-to-roll handling is something we've been doing for many, many years, basically since the beginning. Handling 12-25-12 materials—that's 12 micron copper, 25 micron polyimide, 12 micron copper—has become a very normal thing now in the flex processing industry. It’s now pretty standard and almost every handler in the industry can do that reasonably well. The problem is that, once you start processing at high throughputs, you're moving the material very quickly and the roll-to-roll handler needs to be able to keep up with that fast movement. When you talk about thinner and thinner materials, which we're processing more frequently now, those thinner materials are more prone to wrinkling and stretching.

A lot of our customers have run into issues where they can no longer keep the tight tolerances they need and the accuracies they require as they go to these thinner materials, because the material starts warping. We decided that this was an ideal time to bring to market, together with our partner Northfield Automation, a roll-to-roll handler that addressed the problem. And we believe that the ESI RollMaster is the solution to the problem of processing the thinner and more sensitive flexible circuit materials at high throughput. It has a very responsive “dancer,” which is basically the part of the roll-to-roll handler that responds quickly to motion by the stage inside the laser drilling tool. As the stage moves back and forth, the dancer has to maintain the tension on the roll-to-roll material.

Starkey: Just to be clear, are we talking about machining on a constantly moving web, or in a step-and-repeat mode?

Riechel: It's a good clarifying question. The ESI tools have a patented compound beam positioning technology, which continuously moves the stages, the galvanometers and, in our case, also acoustic optic devices on the 5335 and GemStone tools. What happens there is, because you're moving these three beam positioning technologies at the same time, you have to move the material back and forth continuously. It's not just moving in one direction, as you would with most wet process technologies, for instance. You're actually moving back and forth, forward and backward, continuously.

The challenge there is that you have acceleration and deceleration that is, in some cases, random and very fast, and the web handler needs to be able to compensate for that continual acceleration and deceleration, and do so very responsively. If it does not do it very responsively, the result of that can be wrinkling of the web and other types of stretching issues. The reason being, if the dancer is dragging against the motion of the stage, you are pulling here going one direction and pulling by the dancer in the other direction, it can cause stretching or wrinkling.

Starkey: What sort of position or tolerances are you able to achieve?

Riechel: The 5335 flex processing product family for ESI maintains processing accuracies of 20 microns. After aligning to all of the alignment points on the material, we maintain plus-minus 20 micron accuracy.

Starkey: Across what width of material?

Riechel: That is across the entire panel processing area, which we do up to 533 x 635 mm.

Starkey: Are we talking purely about a drilling operation or are we talking about a part drilling and part profiling operation?

Riechel: We have the ability both to drill and do routing or profiling. Typically with roll-to-roll processes, however, you limit yourself to drilling because if you cut out profiles, then where does the cut-out material go? You could get around that by having laminated PET material on the bottom of your flex material. Some customers do that, but more often they will do that sort of routing or profiling operation in panel format because then you're loading manually, you take it off and then you can remove the excess material from the work table afterwards.


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