Homebrew PCBs

Andrew Volk:

You are quite right. I also worked in the semiconductor fabrication 
domain for a while,
and we used spin-coating with the old Kodak KPR, and other resists which 
were
applied using a professional spin-coat machine.

The wafer was placed on the turntable. A drop of resist was applied to 
the center (approx)
or the wafer. The motor was turned on, and the resist was thrown across 
the surface of
the wafer very, very evenly.

The turntable rotated at high RPM for only a second or two.
Yes, sometimes the resist splashed out onto the wall of the spin-coater.


The "dip tank" method is very successful for coating large PCB panels.
The size of the panel is only limited by the capacity of the dip tank.
Usually, the "pro" machines have a controlled withdrawal mechanism
which assures even coating.

Roland F. Harriston, P.D.
***********************



On 4/6/2013 11:08 PM, Andrew Volk wrote:
>
> Spin coating is uniform enough that it is also used in the 
> manufacturing of
> silicon wafers for integrated circuits. You want to talk about holding 
> fine
> lines? Try 50 nanometers. That is 500 Angstroms, 0.000002 inches.
> Spinning works.
>
> From: Homebrew_PCBs@yahoogroups.com 
> <mailto:Homebrew_PCBs%40yahoogroups.com> 
> [mailto:Homebrew_PCBs@yahoogroups.com 
> <mailto:Homebrew_PCBs%40yahoogroups.com>]
> On Behalf Of Boman33
> Sent: Saturday, April 06, 2013 10:48 PM
> To: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com>
> Subject: RE: [Homebrew_PCBs] Re: Seno 100 photo resist applicator
>
> I know spin coating has been used commercially but it always bothered me
> since I do not understand how it can be a uniform coating. Basically there
> is zero centrifugal force in the center and lots at the edges. How can 
> that
> create a uniform coating?
>
> Decades ago I used to coat PCBs by SLOWLY withdrawing them from a skinny
> rectangular tank which left a uniform coating except the bottom edge.
> Placing the PCB still vertically on a tissue paper drained off the 
> excess at
> the edge.
>
> Bertho
>



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