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Dymax vs Humiseal Urethane Confomals.... Anyone?

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Dymax vs Humiseal Urethane Confomals.... Anyone? | 3 February, 2009

We need to use a conformal product that will hold up in environmental tests, for southern CA weather specifically.

Does anyone have experience with both, which do you prefer? Has anyone seen or had test data for these materials?

Thanks in advance....

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Dymax vs Humiseal Urethane Confomals.... Anyone? | 3 February, 2009

Good morning Jamie.

I work at a CM and can offer some input on process flexability.

I do not have any data on how reliable the coating is but I can say that they are both very difficult to control.

Will you be selective coating or full coating? How are you applying?

We are using A PVA with and Atomize and Dispense valves. When we ran Dymax, we only fully coated with the atomize head. We would mask with rubber boots or plugs or silicone based adhesive tape. It seemed process friendly. We were actually able to run it as a second head with a silicone process in the same machine with no problems of cross contamination and it was compatible with our no clean flux. It was also a UV cured process. It is amazing that coating can cure that fast 12 seconds a board. It was not good for and Hand solder repair after it had been coated. It was super hard. Smelled awfull.

The 1A33 was a different story. Very tempermental coating. I have spent days and days setting up this process. You will need to research the compatibilty with your No-Clean process smt/wave if you have one.

We have a customer that has some very demanding keepouts. The most difficult part about this particular coating is its atomized application and it is similar to water or alcohol in viscosity.

The dispense is ok. We run a 9-1 mixture and it applys pretty well. Needle maintenance is my only gripe really.

We have struggled with the solids in/solids out portion of the atomize application. We noticed that anything over a 50%/50% mixture of solvent to coating would result in icicles forming out of the end of our atomize head some times as long as a quarter of an inch(imagine the spray pattern on that one!.)

We are trying to reach a coat thickness of 2-5 mils per the customer spec. Problem is we are putting on around 12 mils wet film due to the 22% of solids in the coating to achieve the dry film thickness. If you have vias that arent filled, the coating will flow through. So, we tried to reduce the solvent load, increase the solids...No good.

You must maintain the needles in your atomize valves constantly also... It is a fresh oxygen cure coating. You will experience the same icicling in that instance also. The coating will allow you to get no-where near a silicone process. With speaking to the engineers at Humiseal, it is due to the surface tension of the coating. (Same reason it flows through ity-bity vias.) Same thing with debris on the board. Unfortunately, I can not be specific about the debris. We never found out what was on our trial boards. You can end up with fish eyes on the product. This also means you can not use normal masking tape. You will need to use a tape that has an acryllic adhesive. (board labels are the same also.)

Another issue, some manufacturers use a silicone based release agent to eject parts out of there molds. Guess what, de-wetting!

This stuff wicks like crazy. I have seen this stuff walk right up the leads of d-sub female connectors and fill them full! Any smt dip connector, you better forget about coating the leads.

Finally Curing... It is supposed to be a 24 hour air cure. We have set up an IR 8 min profile @95C. Our goal is to make sure all componens are above 95C for at least 5 minutes. After that you still need to handle the boards by their sides. They will need to cool for approx 5 minutes before the coating becomes "handle-able."

I will say also say that you are better off with an IR oven. From what I understand - when you are using a heated fluid/atmosphere (convection)and blowing it in currents around the coating, it will heat from the outside in. This will cause the coating to form a skin on the out side, trapping gasses on the inside - causing bubbles!

With IR you heat from the inside out. Much like the sun and the black shirt. This allows the gasses to push out of the coating and chances of bubbling become less. I would suggest keeping a ramp rate of .5/deg C.


So, I am not knocking 1A33, it is just a difficult coating to work with. Unfortunately, that is the only Humiseal Urethane I have experience with and I am not sure if the others are similar.

I hope this helps and the best of luck to you.

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Dymax vs Humiseal Urethane Confomals.... Anyone? | 12 February, 2009

A few other data points to consider.

My experience working with Dymax 984LVF material was that its UV cure must be initiated immediately after coating, otherwise is surface will remain tacky forever, something like a post-it note tackiness, which will attract dust and show fingerprints to the max.

Another concern is it's secondary cure. It requires a secondary thermal cure to cure areas that are shadowed. That means just about any quad leaded surface mount component. The thermal cure temperature was quite high and had to be held for a period of time; you couldn't cure it at a lower temperature for a longer time; it neeeded that minimum temperature to iniate the shadow cure. The temperature/duration was above that recommended for several of the components we used. There were occasions when we would pull off components for a repair and find uncured coating beneath the parts, months after the initial application. Because the unpolymerized material contains acrylic acids, that's not a desirable siuation. Things get far worse if you employ contract manufacturers to perform the conformal coating. Many of them don't perform the secondary cure or they have operators that believe if what they see is cured then everything must be.

The other issue was that the Dymax didn't like to recoat. It would often bead up if we tried to apply a second coat over the cured product. We ended up standardizing on Dymax for the first application and Humiseal for touch-ups.

In other words, you need to follow the manufacturer recommendations, because even if all seems well, it may not be.

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Dymax vs Humiseal Urethane Confomals.... Anyone? | 24 February, 2009


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