Hi TechNetters,
I sincerely hope you have had a better week than me! However, in replying to
Rick's original question and Martins response, firstly I have replied to
Rick OFFLINE, heaven forbid that I should be accused of
spamming......again.......
However, in respect to Martin's reply:
Auto-Shop spraying for conformal coating?
Please consider that: A true conformal coating should be applied to a
thickness of 0.001 to 0.005 inches dependant upon the material selected.
This should be the thickness applied to a flat, unencumbered substrate.
The profile of a circuit assembly resembles Manhattan in miniature. Have you
felt the influences of high rise buildings on airflow?? Try Chicago then!!
In order to get the coating applied correctly, you need low pressure. Less
than 10 psi. You then need to get the coating UNDER (as far as possible) the
components and to make sure that drips, runs, blisters and other coating
deformities (look at IPC-CC-830) are minimised.
Will your "Auto-booth" spray be wet or dry back? Is the exhaust at the rear
or under the assembly? Will you spray vertical or horizontal? What spray
pressure and what coating blend will you use? What sort of coating?
Most folks can easily spray coat a flat surface, now try 3D!
I do not wish to give away all our secrets but, as with most things, there
are tricks to every trade.
If you are handling 2 part materials, for goodness sake do not (no, on
second thoughts PLEASE DO) dip coat 2 part materials. The wastage will help
ease me into early retirement.....
Spraying is the only practical and cost effective method for 2 part
materials.
Dipping inexpensively? Well, provided your assembly has been designed for
coating (all non-coat areas on one side of the board) then I can dip coat
under as well as over components, up to 500 assemblies per hour at a far
lower cost than any other method. Of course curing needs to be considered.
UV curing? I have posted other replies on this topic but: if you are coating
2 dimensional objects, this is a great technology. If it is 3 dimensional,
Einstein had it right, more or less, "Boy, is it difficult to bend light!"
However, and without wishing to be flippant, the issue with UV materials is
pot life and stability to ensure shadow cure. "Cure under the device? No
problem but pot life will be but a few hours! Otherwise, curing will be
generally around 48 to 72 hours AFTER the UV "CURE" part.
Fibre-Optics, Track-side coating or other 2 dimensional objects - UV is
great.
However, also remember that the time it takes to apply the coating really
does not change. So, the speed of the conveyor is dictated by the dipping
time NOT the curing time and don't put the curing zone anywhere near the dip
tank or you will have a wonderful, if expensive, paperweight!
Regards, Graham Naisbitt
__________________________________________________________________________
[log in to unmask]
Concoat Ltd
Alasan House, Albany Park
Camberley GU15 2PL UK http://www.concoat.co.uk
-----Original Message-----
From: Martin <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 18 June 1998 23:04
Subject: [TN] Conformal Coating
>Rick,
>
>Interestingly enough, my company is researching the possibility of setting
>up one of our vendors to do Conformal Coatings for us!
> Many coating materials can be applied with same sprayers used in
>auto shops. The minimum of equipment, spray booth, compressor, and hand
>sprayer, will cost $3500 if you go this rout. Just check out a Grainger
>catalog. Don't forget to add the cost of installation, local environmental
>requirements (always ask before you buy), and training into your
estimation.
>In any case, you are still in fairly good shape money wise. This kind of
>system is not very good for the 2-part coatings, but not many people are
>requesting that anyway. By the way, it was a rep from a coating maufacture
>who told me about this.
> I don't know of an inexpensive way to dip coat.
> On the other hand, if it is certain that your company is going for
>the long run, you might move up from the economy car, to the Cadillac.
Hague
>makes a stand alone system that looks pretty impressive, but so is the
>price. Starting in at about $13,000 with the bells, but without the
whistles
>it is quite an investment. I think the system was called the SB-2900.
> You will have to anticipate the coatings you want to offer your
>customers as the curing conditions is a definite factor. You might need UV
>lamps or ovens for the initial cure.
> Pitfalls, well we haven't tried it yet. One of our other vendors
>does offer Conformal Coating and it is looking like we will shift
production
>over to them. There are other reasons for the move besides this one, but it
>is a factor.
> As a final thought, check out the archives for this forum. There is
>a ton of usefull information there.
> I realize some of this is obvious, but I am coming from the
>perspective of a customer, not a supplier.
>
>
> Martin
>
>----------------Original Message---------------------------------------
>Date: Wed, 17 Jun 1998 20:09:56 -0700
>From: Rick Thompson <[log in to unmask]>
>Subject: Conformal Coating?
>MIME-Version: 1.0
>Content-Type: text/plain; charset="iso-8859-1"
>Content-Transfer-Encoding: 7bit
>
>Hi Technetters,
>
>A number of our customers are starting to request more conformal coating of
>the PCBA's we assemble for them, and I have been given the task of
>evaluating various materials and equipment for doing this in-house rather
>than outsourcing it. Specifically, I looking for any help or pointers I
can
>get on sources of equipment, specific types (SR, etc) I should consider,
>environmental and health concerns and regulations, etc. Spraying appears
to
>be our best application method at this point. Any comments on building a
>spray booth vs. purchasing a unit from one of the vendors supplying these
>would also be appreciated.
>
>Thanks in advance for any tips you might provide.
>
>Regards,
>
>Rick Thompson
>Ventura Electronics Assembly
>-------------------------------END------------------------------------
>-------------------
>Martin Spizman
> MEYER SOUND LABS
> (510) 486-1166
> [log in to unmask]
>
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