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SMT electronics assembly manufacturing forum.


Coatings to prevent water ingress

ramanandkini

#24592

Coatings to prevent water ingress | 24 May, 2003

We have an electronic circuit with a miniature stepper motor, quartz crystal, Electrolytic capacitor,chip resistors and few smt LEDs. The PCB material is CEM1 with SMOBC and HALS finish. This circuit is assembled in a plastic casing and goes in to a car as a dash board instrument. Now it has to pass a water ingress test. The spec for the water ingress test is that 2 drops of water per sec is made to fall on the instrument (plastic casing) and the instrument has to run for atlaest one hour. Our circuit has failed within 15 minutes since there are gaps in the plastic casing. Water has entered the electronic circuit and shorting has taken place. Provinding gaskets to pass this tests need redesign of plastic casing which is time consuming and costly. We are now looking at some sealants that would totally seal the water entry on to the circuits. Kindly suggest suitable sealants for this harsh environment. Alternately, how this test can be simulated? We have set up a burette with water for this test. Is this right way of conducting the water drop test? Will CEM1 copper clad laminate withstand water ingress test?

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jkhaiar

#24593

Coatings to prevent water ingress | 26 May, 2003

Hi ramanandkini

Is this an Ip 54 or Ip 56 Standard requirement? Can you clarify to which standard you want the protection? Regards

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ramanandkini

#24597

Coatings to prevent water ingress | 26 May, 2003

Hello, I am unaware of the standards that you are mentioning. If you have a soft copy pls. mail it to me. (ramanandkini@titan.co.in) If not, where on the web, these standards are available? All I know at present is that this is part of a Engineering specs given by Ford. regards

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jkhaiar

#24598

Coatings to prevent water ingress | 27 May, 2003

Hi ramanandkini

Here is the link for the document ip reference

http://www.eiema.org.uk/assets/pdfs/IPCodes.pdf

Hope it helps Regards

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#24600

Coatings to prevent water ingress | 27 May, 2003

Take a look at this stuff:

http://cms.3m.com/cms/US/en/2-178/iileuFX/view.jhtml

Its used on boards in beverage vending machines, etc.... not Mil approved but is excellent for commerical apps.

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Mike F

#24678

Coatings to prevent water ingress | 3 June, 2003

Do a search in the archives on conformal coating and silicone conformal coat.

A variety of companies make conformal coatings and the equipment to apply it. Coatings can be applied by dipping the board into the coating, brushing it on, or spraying it on (some coatings are even vapor deposited, but you don't need that type of protection). Machinery is available to partially or completely automate the different application methods.

Different coatings are cured by heat, UV light, chemical reaction (2 part mixes), and exposure to room temp air and himidity.

What you pick depends on your production rate, the end use environment for the product, environmental restrictions where you will be applying the coating, and the skill levels of your operators.

Given your lack of previous experience with conformal coating, I would also look for a coating supplier that has technical help nearby. Check with your other vendors, they can usually tell you what other companies are in the area.

Good luck, Mike

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Ramanandkini

#24682

Coatings to prevent water ingress | 3 June, 2003

We have some experience in manual application of conformal coating using a brush that too for small circuits espceially on the soldered pads. We use Chase corporation's Humuseal 2A64. This passes high humidity tests. I am also in touch with Lackwere Peter's. Now this is for a bigger board and the water ingress test is different from our usual high humidity test. Is there any apparatus that I can use for this test? Right now I have constructed my own. I checked with automobile speedo meter mfrs. They have rain baths, salt sprays. For water ingress they immerse the meters in a tray containing water up to an inch.After posting in this forum I came to know that 3M makes conformal coating that is good for coffee vending machines.

I would be happy if some one could suggest equivalent ASTM/IPC/NEMA standards for this test procedure so that my test method is on par with the international standard.

thanks

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