> On Fri, 6 Nov 2009 17:56:40 -0800 (PST), Greegor <greego...@gmail.com> > wrote:
> >On Nov 3, 1:15 am, Archimedes' Lever <OneBigLe...@InfiniteSeries.Org> > >wrote: > >> On Mon, 2 Nov 2009 22:03:41 -0800 (PST), Greegor <greego...@gmail.com> > >> wrote:
> >> >How do you like getting products made that way?
> >> Unless YOU QUOTE who you are responding to, nobody will know who or > >> what the fuck you are talking about.
> >> Not everyone reads or looks at there news the same way.
> >> Relying on threaded views is retarded.
> >> QUOTE what you are referring to. D'oh!
G > Read the subject title, Archy!
SUBJECT: "PCB Encapsulants to Annoy Copy Pirates" G > How do you like getting products made that way?
AL > Folks respond to the BODY of a post, not AL > the fucking topic title. Those that do have AL > their reward, and are pretty fucking AL > stupid as well. AL > AL > Also, why would some fucking total retard AL > snip the entire body containing the details AL > of what the person wanted to know, just AL > to make a snide fucking peanut gallery AL > comment? AL > AL > Oh... wait... That was a Retard Gallery AL > comment. It's all clear now.
>>> :On Thu, 05 Nov 2009 22:37:53 -0600, Vladimir Vassilevsky:<nos...@nowhere.com> wrote:
>>> : >>> :> >>> :>:>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 >>> :>http://www.abvolt.com >>> : >>> : >>> : Quite simple. Conformal coat the PCB prior to potting. >>> : >>> : Still getting breakage? Conformal coat... twice. Make a blanket.
>>> It is far simpler and more effective to simply dip the whole board in pourable >>> silicone rubber prior to encapsulation with the hard epoxy. That will leave >>> plenty of room for expansion. >> Well ok, as long as the silly-cone has the appropriate thermal >> conduction. I'd order a thermistor measure on the x-PCB to >> verify temp remains happy on power components, if it has any. >> Ken
> You find that out when you beat up ten finished assembly candidates > till they fail. Then find out where they failed and why.
One rude surprise of some conformal coatings: Ferrite beads may no longer work!
Hoo boy was a major Aerospace company surprised when they found this out the hard way.
Apparently a ferrite bead has to magnetostrict to operate per spec. Keep it from doing so and the rules change wildly.
-- Many thanks,
Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: d...@tinaja.com
<dynam...@vianet.on.ca> wrote: >On Nov 8, 12:51 am, D from BC <myrealaddr...@comic.com> wrote: >> On Sat, 07 Nov 2009 22:21:40 -0700, Don Lancaster <d...@tinaja.com> >> wrote:
>> >One rude surprise of some conformal coatings: Ferrite beads may no >> >longer work!
>> >Hoo boy was a major Aerospace company surprised when they found this out >> >the hard way.
>> >Apparently a ferrite bead has to magnetostrict to operate per spec. >> >Keep it from doing so and the rules change wildly.
>> Neato.... >> The material has to move to act like the specs.
>You can use vaseline to maintain the magnetostrictive constant, >constant. >Ken
Silicone dry lube spray, wiped clean. Similar to mold release.
> >>> :On Thu, 05 Nov 2009 22:37:53 -0600, Vladimir Vassilevsky:<nos...@nowhere.com> wrote:
> >>> : > >>> :> > >>> :>:>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 > >>> :>http://www.abvolt.com > >>> : > >>> : > >>> : Quite simple. Conformal coat the PCB prior to potting. > >>> : > >>> : Still getting breakage? Conformal coat... twice. Make a blanket.
> >>> It is far simpler and more effective to simply dip the whole board in pourable > >>> silicone rubber prior to encapsulation with the hard epoxy. That will leave > >>> plenty of room for expansion. > >> Well ok, as long as the silly-cone has the appropriate thermal > >> conduction. I'd order a thermistor measure on the x-PCB to > >> verify temp remains happy on power components, if it has any. > >> Ken
> > You find that out when you beat up ten finished assembly candidates > > till they fail. Then find out where they failed and why.
> One rude surprise of some conformal coatings: Ferrite beads may no > longer work!
> Hoo boy was a major Aerospace company surprised when they found this out > the hard way.
> Apparently a ferrite bead has to magnetostrict to operate per spec. > Keep it from doing so and the rules change wildly.
Beads also make heat when they do it. They are often the most "point source" like heaters in the who design.
>On Nov 3, 7:56 pm, D from BC <myrealaddr...@comic.com> wrote: >> On Tue, 3 Nov 2009 18:22:04 -0800 (PST), "J.A. Legris"
>> <jaleg...@sympatico.ca> wrote: >> >On Nov 3, 7:33 pm, Archimedes' Lever <OneBigLe...@InfiniteSeries.Org> >> >wrote: >> >> On Tue, 3 Nov 2009 07:01:38 -0800 (PST), "J.A. Legris"
>> >> <jaleg...@sympatico.ca> wrote: >> >> >5) Environmentally unfriendly: for you, the customer and everyone >> >> >else.
>> >> Cured potting compounds pose no environmental threat (nearly all), and >> >> even when uncured they only pose a threat to the environment if you or >> >> another of your dopes gets the shit all over the place.
>> >> Use some brains.,
>> >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.
>> I'm wondering about thermal expansion.
>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.
>> My 1"x1" pcb that I want to encapsulate will be in an environment >> where the temp may swing from 22C to 70C daily.
>Smaller is better.
>> 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.
>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.
>>ex: Very very hot melt? Low melting point glass?
>>D from BC >>Amateur smps designer >>British Columbia, Canada >>Posted to sci.electronics.design
>Regular opaque hobby casting resins?
Maybe... The potting should be resistant to a hot tipped vacuum system. The potting potting compound is removed by melting and burning in an archaeological fashion with a hot vacuum nozzle. afaik...the above is doable. If I can make a potting removal tool, the techno duplicators at 'The Happy Circuit Company' can make a potting removal tool.
>>>ex: Very very hot melt? Low melting point glass?
>>>D from BC >>>Amateur smps designer >>>British Columbia, Canada >>>Posted to sci.electronics.design
>>Regular opaque hobby casting resins?
>Maybe... >The potting should be resistant to a hot tipped vacuum system. >The potting potting compound is removed by melting and burning in an >archaeological fashion with a hot vacuum nozzle. >afaik...the above is doable. >If I can make a potting removal tool, the techno duplicators at 'The >Happy Circuit Company' can make a potting removal tool.
Last i saw they were catalytic thermosetting plastics. Not quite to the diallyphthalate class, but pretty good.
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