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44 PCB007 MAGAZINE I JANUARY 2019 electroless copper deposition. You're creating the circuit directly; there's no etching. The circuit is built over the lasered pattern with a full-build additive electroless copper process. As I said, typically these processes have very low elongation, only 1–2% elongation to the copper deposit. The deposits are typically very brittle. Until now, this has been the challenge of this technology for higher reliability applications. For more stringent applications in the automotive space, they need a copper deposit that can withstand thermocycling because the molded plastic will expand and contract as it goes through heat cycles. Essentially, what is required is a copper deposit that can withstand this thermocycling and have enough elongation to withstand that environment. The new process from MacDermid Alpha accomplishes this task with a zero stress electroless copper bath. This means that the deposit doesn't want to blister off the surface; it will remain intact on the surface with excellent adhesion to the substrate throughout the life of the device. The deposit has high elongation so that the copper can stretch without cracking; thus, helping expand the amount of possibilities for MIDs in the automotive space. Holden: You're talking about automotive applications, such as headlight displays on the exterior of the car probably near high heat sources. What kind of testing do you anticipate can handle a stressful application like that? Bernards: One of the typical tests that we do is measure the percent elongation of the deposit utilizing ASTM E-345. For that, we simply deposit the copper onto a stainless steel sheet so that it can be peeled off. Then, we use an inch-round device to stretch the copper and measure how much you can elongate the copper before the deposit breaks. Another test would be a thermocycling test where you put MIDs into cycling chambers, subject them to a number of thermocycles, and then look for cracks in the circuitry. Another simple test that we do is coat the plastic devices and bend the plastic. The plastic is bendable, so we just bend the plastic around mandrels and look for cracking in the deposits. If you perform these kinds of tests on a conventional full-build electroless copper that's used in MIDs today, they will not provide optimal results. Current commercial electroless plating baths are not formulated with these types of challenges in mind. But the new process that we are very excited about passes these tests very well with good adhesion to the substrate. Another thing that is interesting about the new formulation pertains to plating fine-line MIDs with tight lines and spaces. Due to the amount of thickness required by a full-build application, typical electroless copper baths tend to get stray plating on the areas between these tight spaces. This new formulation does not have this problem. We've plated sub-50-micron lines and spaces with the full-build electroless deposit with no stray plating at all to the deposit. Holden: In the past, we saw this with separate flexible circuits and assemblies. Are these enabling any new applications? Bernards: Typically, they are using flexible circuits and connectors to go from position to position where it's a 3D situation not on one plane. MID technology actually eliminates the need to have flex circuitry and connectors all attached to a core circuit board. You can just put the circuitry right into the plastic that is holding the core components of the electronic device—for example, an automotive LED— and the circuitry can pass right through this molded part. It's quite a bit cheaper. Holden: It sounds like an interesting technology. Will MacDermid Alpha have some kind of how-to book for people interested in the The deposit has high elongation so that the copper can stretch without cracking.

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