Stefan Trethan wrote:
> On Tue, 15 Mar 2005 12:05:40 -0500, uhmgawa <uhmgawa@...> wrote:
>
>
>>Alternatively to avoid intricate pump components having
>>to withstand etchant corrosion it would be possible to
>>use compressed air to pressurize a container of etchant
>>located below board tank level. This again is not 100%
>>duty cycle as the etchant must be allowed to gravity
>>backflow to the etchant container when said container
>>becomes empty. Achieving this could be as simple as locating
>>a check valve in the backflow line and bleeding off the
>>air pressure in the etchant container. The only thing
>>required to automate the process is a float switch in the
>>etchant container and a solenoid air valve to alternatively
>>pressurize/bleed air to/from the etchant container.
>
>
>
> Had the same idea a few days ago. However, will try rotational etcher
> first.
> Nozzles need quite a lot of volume.
>
> ST
I've spent six months (spare time project) building a spray etcher. From
what I've learned, about spray nozzles and spray pumps is they need at
least 1 bar to get reasonable spray patterns and distribution from the
nozzle. For anyone wanting a HCl/CuCl resistant pump capable of > 1bar
and not expensive then I suggest looking into FloJet recreational
vehicle pumps. The other competing brand is Shurflo, but DO NOT use
these pumps as they have a set of stainless steel screws that fasten the
pistons to the diaphragm. According to Shurflo customer support, all
models are constructed in the same way. The heads of the screw will
erode in several weeks as I found out the hard way. Fortunately I was
able to replace the screws with standard M3 machine screws which I
coated the heads in polyethylene plastic. My modified Shurflo pump has
now been operating for several months without problems. I believe the
FloJet brand do not suffer from this drawback as the pistons are
fastened using a different method. There is really no other alternative
to a pump suitable for a hobby spray etching tank. If not then I'd love
to know about it. The pumps are also available in slightly larger
versions intended for industrial use, but double the price.
My spray machine does 1 minute etch per side using CuCl, S.G=1.33, 25°C,
Cu foil thickness 35um, spray pressure 1.9 bar , pump 12.5V at 5.5 Amps
, 3 nozzles spanning a continuous line 300mm across the PCB.
http://www.flojet.com/prodInfoApp/servlet/DisplayProducts?typeId=FRQSP&page=0&catalogId=RV&categoryId=FRMPU&companyId=FLOJETAdam