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Urethane Coating (1A33)

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Urethane Coating (1A33) | 25 August, 2008

I have a question for the manufacturing masters...

We are going to start running test trials/DOE of a Urethane Coating (Humiseal 1A33) and I am not sure what to expect. From what I understand, urethane coating is pretty difficult to work. It is supposedly a very watery coating. We are using a PVA automated spray/dispense coating machine. I am very familiar with Silicone based coatings which are thicker and easier to control.

Does anyone have recomendations on where to start my DOE with this material (or similar materials)?

Meaning, speed, Z, curability, etc...

What are some of the process defects that you noticed with the coating?

Are there any positive points or angles about the urethane coating that I can manipulate in my programs? From what I understand, there is no oven cure according to the datasheet on this product, but, our customer is recommending that we have one... Any ideas why?

As you can tell, I am in the dark on this one and could use the help.

Thank you kindly


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Urethane Coating (1A33) | 26 August, 2008

I am not positive about this but I have been told that you cannot use acrylic and urethane coatings in systems that have had silicone run through them. It was explained to me that you can never fully get the silicone out of the existing system and that it will contaminate the other coating and you will get sever dewetting issues on the boards you try to coat. I'm not 100% sure this is true, as I've never had to run silicone through our system, but I believe that is what I was told by the person who trained me on the machine.

Other than that I've never worked with silicone coatings so I can't really offer you any comparisons. I can tell you that your customer probably wants an oven cure because if you let 1A33 air dry it can pick up and orange tint, while oven drying tends to leave it crystal clear. In my opinion it can be a pain to clean off the boards once completely hardened. I recommend picking up the manufactures recommended remover in case you have any problems or need to spot clean to remove a part.

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Urethane Coating (1A33) | 26 August, 2008

hey, thanks for the advice.

We have replaced all the lines and have had the valves cleaned & rebuilt, so we are hoping that will be sufficient.

What does the dewetting of the urethane coating look like???

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Urethane Coating (1A33) | 27 August, 2008

Contact Graham Naisbitt he is an expert in this field.

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Urethane Coating (1A33) | 27 August, 2008

Thick, hard conformal coatings of acrylic, urethane and epoxy have a well documented history of causing solder joint cracks and breaking glass/ceramic and other brittle components. Dissimilar expansion and fairly high surface bond strengths of the materials cause this problem. Controlling the thicknesses of conformal coats as specified in J-STD-001 is safe, but thicknesses greater than 0.010" begin to be a problem. Some of the softer urethanes in the Solithane and Uralane series seem to be less succeptible to these problems.

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Urethane Coating (1A33) | 27 August, 2008

Thanks Patrick. I will probably contact him tommorrow.

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Urethane Coating (1A33) | 27 August, 2008

Silicone contamination could appear as fisheyes or dark spots under UV light. 1A33 can be heat cured but is a single component oxygen cure coating - it needs a source of oxygen to cure. An unvented oven may slow or limit the cure. Check out the TDS - 20hrs at 190C, 30hrs at 170F, or 30 days at room temp for "optimum" properties. Does PVA or Humiseal have any application advice for 1A33 in your equipment?

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