Conformal coating needed for BCMs?

[iamyo]

Hi,

I work for a Tier1 supplier of BCMs. All our BCMs are coated during the manufacturing process. We do this because, historically, it was the only way to meet customer requirements (Humidity tests, Dewing tests, Salt Spray, ...)
Recently, several OEMs are requiring to remove the coating but still is Tier1 responsibility to meet reqmts.
I know there are techniques to make more robust designs (avoid high impedance points, increase tracks distance with high differential-voltage, ...) but I am still not confident that we will meet these reqmts.
We dont perform any type of cleanning to remove contaminaton during manufacturing process which also does not help.

Any expert or any engineer who has experience about this?

Thanks
iamyo

 

[Comcokid]

In the long past, I worked for companies that made gauges/circuit boards for insturments - for industrial vehicle and marine markets. With thru-hole, careful design to avoid high impedance nodes, and attention to layout you could make non-coated electronics. But it required cleaning the boards and attention to the enclosure design - usually plenty of vent holes to allow condensing moisture a way out.

I have done uncoated industrial electronics and once had a condition where a SMT no-clean solder and water wash resulted in conductive comtamination that caused the uP circuit to draw excessive sleep-current and problems with analog nodes of only 100K impedance. A fortunate problem as subsequent test showed that the particular no-clean and long exposure to humidity would have created the same condition. A board lot had to be re-cleaned in alcohol to fix, and the solder paste had to be specified to avoid the issue again.

 

[DRWeig]

What's a BCM?

It's best to spell out your TLAs. I'm not familiar with that one, and Google tells me it's the Baylor College of Medicine.

Good on ya,

Goober Dave

PS -- TLA = Three Letter Acronym

 

[MacGyverS2000]

board control modules?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[iamyo]

Sorry! BCM stands for: Body control module or Body computer module located in the passenger compartment of the car. In general my question would be valid for any electronic module located in the passenger compartment.

Thanks

 

[iamyo]

Comcokid,

interesting answer. Let's say that you agree with me that removing the coating and making a great robust design would still not be sufficient and we would need some cleanning process right?
I was thinking in ways to also avoid cleanning process therefore saving this high investment.


Thanks

 

[MikeHalloran]

>>>several OEMs are requiring to remove the coating but still is Tier1 responsibility to meet reqmts<<<

Apparently the last round of layoffs got the guys who knew what the hell they were doing, and now you're getting stupid/conflicting orders from new grads, or worse, MBAs.

Good luck.



Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

I expect it's the requirement has more to do with RoHS, end of life recycling, VOC's etc. etc. handed down by bureaucrats.

 

[DRWeig]

I would have to learn a bit more (following MikeHalloran's thoughts) about WHY the company wants the conformal coating removed? What are they trying to accomplish?

If it's simply for cost savings, I don't think they've evaluated the alternatives very thoroughly...

Good on ya,

Goober Dave

 

[iamyo]

Well, the answer to "why" is cost. They want to reduce cost at the minimum level! So they give you lower target price in the competition due to the fact that no conformal coating is included... but it's your responsibility to meet rqmts. I hate them! And you never know whether your competitor is able to remove it, therefore offering lower prices.
The OEM says the rest of the electronic modules in the passenger compartment are not coated (which I dont believe)...

Difficult decission.

 

[MikeHalloran]

If they're using electronics that are not coated, they're doomed.





Mike Halloran
Pembroke Pines, FL, USA

 

[DRWeig]

Agree with Mike!

Good on ya,

Goober Dave

 

[Comcokid]

iamyo - what I've indicated is that you can do no-coating in some cases, but it takes a long time to work out just how you will carefully approach it for a particular application. For the gauge manufacturer it took several years of trial and sometimes error to get it right, and some produced product generations that weren't real great. It was undone by critical components being no longer available in thru-hole. Even the PCB had to be CEM1 (appliance board) from certain manufacturers. Many FR4 if they got wet (marine salt environment) would wick moisture/salt up any glass fibers that were not completely saturated with resin.

The thing is, you can test to the 'environmental specs' you may have, but frequently they do not represent the edges of the bell curve of the real world. You meet the environmental specs, you cover your butt, but if you don't cover the real world, you will eventually piss-off the customer and end user/owner.

And, your BCM may be in the passenger compartment, but having lived in Florida you find there's nothing like a car that has had it's carpet shampooed and then been in the hot Florida sun - a sauna with >100% humidity. And you can re-create this situation daily if you crack your windows to let heat out and you have one of those frequent afternoon showers. Air conditioners are not for reducing the heat so much as they function to pump humidity out. You get similar humidity situations at lower temperatures in the Pacific Northwest (Portland, Seattle, etc). Not everywhere is like Michigan, or the other climates where automotive design is done.

As I recall (its been some years) industrial manufacturers like JD, Cat, etc required their uncoated PCBs to be tested for ionic contamination similar to mil-specs, and many of these boards would be fully potted and encased.

 

[theoldwizard1]

I concur with Mike "They're doomed". With surface mounted devices and lower (3V) uP operating voltages, experience tell me the ravages of time and moisture will kill you.

Years ago, when ECM where very new technology, the company I worked for, switched from a split pin and socket connector to an edge card connector simply because upper management found out is was cheaper. We did not have time (or manpower) to prove them wrong. That experiment lasted 1 model year.