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Over the years, engineers wrestled with the problem and attempted several corrections:
- Heavy duty rolls were made with stiff and stronger shafts to minimize the bend.
- Rolls were tapered to provide a slightly larger diameter in the center and graduating smaller to the ends.
- A cantilever mechanism was patented in an attempt to counteract the roll bending. The problem was better, but not fully corrected.
These attempted solutions failed to eliminate the shortcoming.
Figure 3: The elegant solution.
Consider a stainless steel, heavy barrel drum applying pressure onto a standard-type rubber roller. Internal infra-red heat, controlled and evenly distributed inside the steel drum, transfers directly to the rubber roller providing optimum distribution of heat and pressure—almost no traditional hot roll bending. Further, if it is detected that there is some bending, which would have minimal effect on the smallest micron features, there would be an option to taper the steel drum to the point of optimizing the even-pressure requirement.
Another feature and machine by-product of this solution demonstrates how a standard rubber roller could be simply replaced due to damage or if a different durometer rubber is required for certain applications. This is just what the doctor ordered for applications like flex circuits and high-profile features requiring special film conformance to the copper.
Figure 4: Pressure, temperature, and rubber roller module.
It is comforting to see that these types of innovations are helping the PCB packaging industry keep up with the most stringent requirements. This is not to say we have solved all the problems because the final PCB still has to wrestle with other issues like chemistry, drilling, registrations, etc., but we have come a long way in the imaging department from stick-on, taped artwork.
Figure 5: Comparison of the pressure results of standard hot roll mechanism to the new drum roller.
Figure 5 compares the pressure results of standard hot roll mechanism to the new drum roller.
There is a distinct difference in the pressure applied and the pressure profile results.
Currently, there are further and complex tests being performed on certain types of laminate and copper surfaces with various types of dry film. We hope to show how our industry is finally adapting to reaching a high level of success with micron features and overall optimal adhesion and attachment of dry film resist to varying copper surfaces.
Our next article will deal with the results of these tests. We will take an exhaustive look at the testing of certain types of dry film and certain types of laminates and copper to document the results of this new innovation. Because of the nature of the innovation, we are expecting outstanding results to transfer those micron features with very high yield.
Fred Long is in business development at Matrix Electronics. To contact Long, click here.
Reference
1. “Improving Dry Film Lamination Yields,” by Jeffery G. Stark, Sensor Products Inc. and Karl Dietz, Printed Circuit Design and Fabrication, Jun 2009.
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