Brian
I cannot let this one go unanswered.
You said:
I agree with you that coating is often necessary or desirable and, in these
cases, the price has to be paid. However, if you think it costs only 5 cents
to clean correctly and coat correctly a board of any size, I'm afraid I am
far from being able to agree with you.
I said coat. I did not say clean and coat.
Quite frankly, the point I was making is that anyone who coats unnecessarily
is wasting money and frequently a lot of money. And anyone who botches the
job with half measures is wasting even more because he will not only have to
pay for the coating materials and process, he will not gain anything in
reliability or anything else.
I understand your remarks but there is not an issue of whether I think
coating can be done for $0.05 per assembly - I know!
As an actual example which might prove useful to those engineers asked to
calculate these things:
500 assemblies per hour, size roughly 3 inches x 3 inches (75 x 75 mm).
Application: automotive.
Design ensures that connector is on one side of the assembly so that dip
coating can be achieved (Designers please note!)
No masking but tooling is required to permit 30 assemblies onto individual
tooling bars.
Production is 24 hours per day 6 days per week plus part shift on Sundays.
Weekly production around 75,000 units.
Annual production around 3.75 million units.
Now, coating material coverage represents 0.0015 inches (38 microns) on flat
area = x 3 around components. Assuming 35% solids I calculate 546 units per
litre. That is 2066 units per Gallon US. Everyone can now calculate that out
according to the price they pay for their coating material. Wastage? Not
much if it done correctly.
Now the equipment. In-line dip coater say around $120K amortised over 3
years = $40K per annum. This equates to $0.01 per unit produced. To which
power has to be added and 1 operator to load/unload system at 500 units per
hour (easily!). Each tooling bar is processed every 3 minutes.
If you run that lot out, you will find that my $0.05 ain't too far adrift -
but it depends what you pay for material which of course, depends upon how
much you buy.
In my opinion, if coating must be done, it is a costly process because
- the whole process must be qualified from a to z
Agreed but that isn't the exclusive domain of conformal coating!
- the boards to be coated must be provably clean, even under the components
Not true. There are many who run no-clean successfully under a coating.
- they must be provably dry and even dehumidified
If you clean yes, dry - dehumidified, in most cases no.
- the coating material must be correctly prepared
What do you mean? Many coating users now buy materials pre-blended for
direct use. Otherwise the system will adjust automatically.
- the coating equipment must be perfectly clean and free from any residues
from previous operations
Que?
- the coating process must be done under strict QC conditions in a dust-free
zone
Hands up those who manufacture reliable electronics in a dirty factory? I
agree that the coating machine should not be located alongside the
coal-fired boiler.
- curing must be done under dust-free conditions
Usually this is "in-system" controlled. Those who do coating at low volume,
use drying cabinets. Still not a major investment.
- the degree of curing must be controlled
Que? Too fast a cure may be bad, but that depends on your material.
Whether the assembly is dipped or sprayed, there is considerable wastage of
coating material.
I don't think you selective coating boy's out there would agree with that
one? Dipping I can assure you has minimal wastage. For more on that one,
contact me off-line.
One must not forget the environmental and H&S aspects either. Many of the
uncured coatings contain such very toxic nasties as toluene
diisocyanate, epichlorohydrin and tetrabromobisphenol A and their sisters
and their cousins and their aunts. They often contain VOCs,
including all the single component systems which, by definition, cannot use
reactive solvents. All this means that emissions must be controlled and,
especially, operators protected (and a white face mask is useless against
toxic vapours). Not to mention the disposal of excess coating materials and
VOC cleaning solvents, which are hazardous wastes.
Modern coatings don't necessarily have such "toxic nasties". Of course you
would have to include paint and flux and adhesives and underfills and paste
and wire......come on. By your analogy, the board fabrication business
should have been shut down years ago.
There are new solventless coatings, water based coatings and (in the USA)
VOC free coatings. For the record, we in Europe do not have a list of
"exempt" VOC solvents, for us a VOC is any solvent that has a vapour
pressure > 0.001 millipascals which includes Gin, Vodka, Brandy and Whisky
aaarrrggghhh!
Of course everyone should maximise their efforts to clean-up the
environment, only problem is the cost for doing so - Oh! Oh! That brings us
back to costs of......
As for the legal aspects, I know of no case where "you may be compelled, by
law, to coat". You mean a parliament has passed an Act or a Bill saying that
you shall coat an electronics assembly, in fault of which you are liable to
a fine or imprisonment? This is purely a civil matter, covered by contract,
whereby the person purchasing an assembly from you may require a coating. If
you don't coat correctly, you are in breach of contract but you have not
broken any law. The only legal aspects involved are those relating to the
environment and H&S, where such are applicable.
In the USA it is a mandate that domestic appliances be UL approved. Without
it, you cannot import.
In Europe we have CE with similar rules.
I have no vested interest in either coating or not coating. It is rather
like post-soldering cleaning or not cleaning. I tell my clients that if
they have imperatively to do one or both, do it well and pay the price for
doing it well but, if they do not need either, then bully for them.
No argument there. Your comments however, leave many with the wrong
impression about cost.
I should also point out that your comments re consumer goods display a
certain dose of cynicism.
WRONG! There are manufacturing requirements properly documented for those
that manufacture Class 1, 2 or 3 products. The test requirements for each
are different - why is that?
I hope you will excuse me for removing the remainder of that message, but I
think this might have bored the pants off most folks by now.
Regards
Graham Naisbitt
[log in to unmask]
Web: www.concoat.co.uk
Concoat Ltd
Alasan House, Albany Park
CAMBERLEY GU16 7PH
Tel: +44 (0) 1276 691100
Fax: +44 (0) 1276 691227
>
> Ken
>
> Contrary to Brian's comments, Coating can SAVE your business
>
> Save: Because you will have fewer field failures
> Save: Because field failure could very well put you out of business
> Save: Because if you design for coating, the cost is minimal v the benefit
> Save: Because you may be compelled, by law, to coat - now why do you
suppose
> that is a mandate?
> Save lives! - Circuits that are safety critical such as ABS, Air Bag or
> Avionics systems, or weapons systems - where did my nuclear missile go?
How
> about utilities such as gas, electricity and water meters that often have
to
> survive for 20 years - GUARANTEED!
>
> I might also point out - and others will correct me if I am wrong but - an
> automobile could be guaranteed for more than 10 years if only the
> electronics systems would last that long.
>
> Come on Brian - your comments are not entirely fair. It is true to say,
> no-one wants to coat but it need not be such a painful experience - what
> price safety? Is $0.05 per assembly a high price to pay? - Play-station,
TV,
> Mobile phone, Computer OK, don't coat, after all, they would prefer you to
> replace the unit.
>
> I hope this helps you Ken but if you would like more, let me know
>
> Regards
> Graham Naisbitt
> [log in to unmask]
> Web: www.concoat.co.uk
> Concoat Ltd
> Alasan House, Albany Park
> CAMBERLEY GU16 7PH
> Tel: +44 (0) 1276 691100
> Fax: +44 (0) 1276 691227
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Ken Patel
> Sent: Saturday, December 16, 2000 01:29
> To: [log in to unmask]
> Subject: [TN] Conformal Coating...
>
> Guys,
> What are the pros and cons of Conformal Coating on PWAs? Who are vendors
in
> San Jose Bay area?
>
> re,
> ken patel
>
>
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