On 7/6/02 8:25 pm, "Peter Lee" <[log in to unmask]> wrote:
>
>
> Technet,
>
>
>
> Can anyone share their opinion and experience on dipping Vs spraying conformal
> coating on PCA?
>
> In terms of :
>
>
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> - Process setup and labour cost
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> - PCA preparation and coating material consumption
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> - Automated Vs manual application
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> - Quality and reliability
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>
>
> Rgds,
>
> Peter
>
>
> Hi there Peter,
>
>
When you are applying a conformal coating, it usually follows that you are
seeking protection under as well as around components. To get the best from
a coating, it should be applied as close to an homogenous film as is
practicable, and at a thickness that is usually in the range of 0.002 inches
or 50 microns +/- 0.001 or 25 microns on a flat unencumbered substrate.
With these in mind, logic would dictate that the best and most efficient
method of application is to dip. Slow in at typically less than 12 inches
per minute so you donšt entrap air underneath components; slower out, at
least slower than the cascade effect of the coating itself which will be
generally around 4 to 6 inches per minute. Both sides of the assembly are
coated simultaneously and several assemblies may be coated at the same time;
400 to 500 per hour is quite common.
Most commercial dip coating systems are able to provide dipping accuracy to
around +/- 0.02 inches or better. This means they can dip up to a particular
connector base and thereby eliminate any and all masking.
A good dip coating operation will cost you less than 15 cents per assembly
that is ALL costs: coating, jigging, capital amortisation (ROI) and running
costs.
HOWEVER, you do need to design for the process. Any masking is a real time
consuming, therefore expensive operation.
If you canšt do this, then spray but use a machine rather than a human who
tend to err! Robotic systems are ideal when you have only selected areas to
be coated or where masking would be a veritable nightmare. However as with
all robots, these are not cheap but they are very effective and efficient.
They have to coat one assembly per pass and one side at a time, so they
cannot match the performance volumes of dip coating.
Otherwise, you are looking at manual spraying plus masking. This may be
ideal for low production volumes and for coatings that may not lend
themselves to dipping such as 2 part urethanes etc.. They will require
careful process control especially on a Monday morning and a Friday
afternoon! :-)
In terms of reliability and quality if you apply the coating using a hose,
but the assembly passes your testing, then this may be a perfectly
acceptable application method and I want to be the coating material
supplier!!
Basically they all work very well, but I think that dipping gives you fewer
process issues and its inexpensive. Spray when you have masking unless the
components required for masking are at one end of the assembly (in which
case dip.) Use the robot if you have the volume and investment finance
available.
Hope this helps
--
Regards, Graham Naisbitt
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