PCB Encapsulants to Annoy Copy Pirates

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I did, which is why I no longer use potting compounds. The problem is dopes like you who cannot reason beyond their next paycheck. The long- term effects of most synthetic chemicals have never been comprehensively assessed, so erring on the side of caution is the wise thing to do.

-- Joe

I'm wondering about thermal expansion.

My 1"x1" pcb that I want to encapsulate will be in an environment where the temp may swing from 22C to 70C daily.

I have no idea if an epoxy encapsulant will flex with heat and shear forces will push on the tiny smt parts.. I'll try to find specs. Perhaps testing in an environmental chamber is needed. But I'm cheap, so I'll be using a light bulb in a box controlled by a thermostat.

Some of us? You're a goddamned idiot for that snide remark. ALL of us like just statistics.

Yes, but you apparently have no clue about hard potted devices.

If it is that small a device, you should already know all about every failure mode there is for it, and that should be able to be determined without examination in many cases. All you should need is your prior knowledge of the circuit operation and the particulars of the failure.

If it is a power supply device and it is failing, you should not be selling it as a product to begin with. A PROVEN design, will have all of its failure modes documented. Any potted design should be a proven design, especially if the potting is meant for IP security purposes. Otherwise, a serviceable potting would be needed.

If you are selling hard potted products, you have already resolved to full replacement upon failure.

Why a PS device would need IP security is the real question. Why this dope thinks his supply circuit is so special that someone would be on his heels to copy it is beyond me. If it is that revolutionary, he should patent it, and SELL the design to a bigger player in the industry.

DUH.

You're a goddamned retard.

Not with a dope like you at the wheel, but yes, there are long term studies, and there is long term knowledge in the industry, you stupid pussified twit.

You're a goddamned long term stye on the face of intelligent men of the world. You meant to say "Being a PUSSY on the "side of caution" is a stupid way to achieve 'progress'".

You are probably so retarded that you embrace RoHS, and you think that metallic form lead is a problem for the environment.

If it were, the lead levels in water tables around lead mining and also around land fills and especially around decades old police shooting ranges would show higher numbers and they do NOT.

Idiots like you are pathetic.

The expansion numbers on potting are for what happens during curing.

Then conformally coat it BEFORE you pot it.

They are, of course, available. Stycast is a common potting media.

Not likely. A simple chamber with known temp is fine.

OK.

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You can find the thermal rate for most materials. There is likely to be a temperature gradient but it will be smaller than the total swing.

Smaller is better.

If you put a very flexible layer over the parts it will help. Unfortunately it also provides the nice parting line to let the pirates pop it apart along the boundary.

I have used a "light bulb" based heat box. Mine used power resistors. You can get thermostats that can switch the load. A couple of jugs of water in the hot box helps to hold the temperature steady.

Run you freezer down as cold as it can get. Put the item in the freezer and let it soak till it is all the way down. Once it is fully cold move it to the hot box. leave it in the hot box for a day and then move it back to the freezer.

This will quickly show you that the potting was a bad idea.

I've yet to find my design on the net nor in chip form. I figure the lazy cheap 'just in case' action is to pot the electronics in my product until it makes enough money for me to afford a patent guy to do all the patent searching, applying,patent write up,defending,offending and license granting...and maybe to run out to get coffee sometimes.

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IIRC you should apply for the patent before you release the product (or even just keep it secret) or you may lose your rights. This presumes patenting the thing is a good idea in the first place - which is unlikely unless you have deep pockets.

-- Joe

It's not fair if I lose my patentability rights when I'd like to release 200 units for ~field testing~ :) to tweek and finalize the design.

You can tweak the design at the bench by beating the hell out of a few units, and being very good at recording and analysis of observed data.

I'm just afraid my customers might do a better job at beating the hell out my stuff more than I can.. :)

The wikipedia article mentions that you can protect your rights by obtaining non-disclosure agreements.

-- Joe

Not sure why you think black paint increases thermal radiation, but it's certainly not going to stop anyone from copying the design. It may slow them down by about five minutes. Maybe.

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It also makes the board likely to fail. The solvent in spray paint is hard on parts. As a result the product will get a reputation for being crap. Since nobody wants to make a copy of a crap product, people will be less likely to copy it.

:I'd like to pot my smt pcb with the nastiest sh*t possible to make it :hell for copy cats.. : :So far I've found: : :

:'Extremely difficult to remove - grants incredible technology :protection ' : :Besides epoxy.. Are there alternatives? : :ex: Very very hot melt? Low melting point glass? : :D from BC :Amateur smps designer :British Columbia, Canada :Posted to sci.electronics.design

One thing you need to remember.. if there are any heat generating components on the board, encapsulation in a hard compound may cause subsequent fracturing of components or solder joints because they can't expand and contract. This may not be such a problem with smt but it has caused problems with thru-hole components on some pcb's I have repaired.

Since Araldite 2014 (3 types btw)

is a bonding adhesive it may cure to be extremely hard and may not allow expansion/contraction of components. If this is likely to be a problem I would recommend a thin coating of pourable white silicone rubber (or similar) over the heat generating components before applying the Araldite 2014.

I know an engineer who spent many years mixing different compounds and fillers trying to create solid substance with minimal expansion or contraction while it is cured, and which will not rip the components off the PCB because of thermal effects. This is no simple problem.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

: : :Ross Herbert wrote: : : :> One thing you need to remember.. if there are any heat generating components on :> the board, encapsulation in a hard compound may cause subsequent fracturing of :> components or solder joints because they can't expand and contract. : :I know an engineer who spent many years mixing different compounds and :fillers trying to create solid substance with minimal expansion or :contraction while it is cured, and which will not rip the components off :the PCB because of thermal effects. This is no simple problem. : : :Vladimir Vassilevsky :DSP and Mixed Signal Design Consultant :

I entirely agree with you Vladimir... However, depending upon the amount of heat generated or the degree of expansion/contraction involved it may not be as extreme as your engineer friend encountered.

The very first instance of this type of problem which I encountered was in electronic ignition systems from Johnson outboard motors back in the 70's. After dissolving the epoxy encapsulant (that took weeks using an expensive chemical solvent supposed to be specific to this purpose) it was discovered that several soldered joints had failed and pcb pads had actually been lifted from the board by the expansion of vertically mounted resistors in particular. Incidentally, the solvent removed the coatings on resistors and other capacitors so determining values was impossible in many case. I never intended to repair the units but I was interested in the failure mechanism of these units. I communicated my findings to Johnson at the time but I never received any acknowledgement.

Ha.. Copy protection by deliberate low quality.

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Quite simple. Conformal coat the PCB prior to potting.

Still getting breakage? Conformal coat... twice. Make a blanket.