Chris Trask wrote:
>>> I'm very much interested in trying this laser toner transfer method
>>>
> for
>
>>> homebrewing single-sided PC boards, and the thought came to me that
>>>
> perhaps
>
>>> an electric waffle iron would be a more practical alternative than using
>>>
> a
>
>>> clothes iron. With the PC board material and the paper sandwiched
>>>
> between a
>
>>> couple of pieces of aluminum or copper plate, the heat and pressure
>>>
> would be
>
>>> more uniform and it would become a matter of applying the pressure for a
>>> suitable amount of time.
>>>
>> Chris, I have not tried an waffle iron, but I got a 1 inch thick piece
>> of steel (4x5x1 inch) and lapped it to make a very flat surface,
>> attached a thermo couple to it. Using a hot plate to heat the iron block
>> to to the target temperature then placing this on my PCB/toner image
>> sandwich and clamping it with a toggle clamp with about 400 pounds of
>> pressure for about 1 minute (20 pounds per square inch). This gives me
>> consistent results.
>>
>>
>
> That's what I felt would result, and I was thinking that using an
> electric waffle iron would enable you to apply uniform pressure and a
> somewhat controoled temperature. Guess I'll look around the thrift stores
> for one of these and see what can be done.
>
>
>> The target temperature is established for the toner formulation your
>> printer uses. This involves taking an image on a piece of paper and
>> while monitoring the temp of the hot plate, looking at the toner with a
>> magnifier and using a sharp pointed probe and noting the softening temp
>> and the melting temp (my toner melts at about 320 degrees F) The melting
>> temp is when the toner becomes glossy (shiny). The pressure and temp
>> combination will determine the amount of image spreading that will occur.
>>
>>
>
> Okay, that gives me a guideline of how to condition the method that I'm
> thinking of.
>
>
>> On small pitch traces you may adjust the temp/pressure/time
>> combination for best results. For very fine pitches, I use a temp of
>> about 280 degrees (this will just tack the image to the copper) then I
>> take this tacked PCB/toner/paper sandwich and place it on the hot plate
>> and raise it to the toner melting point (without pressure) ... this will
>> cause good adhesion of the toner to the copper with minimum image
>>
> spreading.
>
>
> And that's even better. I'll definitely look for a small electric
> waffle iron and see how to adapt it for small boards. I wonder now if
> adding a thermocouple to one of the plates and then connecting it to some
> sort of controller would help, or perhaps simply measure the waffle iron
> temperature and adjust the time accordingly.
>
>
> Chris
>
> ,----------------------. High Performance Mixers and
> / What's all this \ Amplifiers for RF Communications
> / extinct stuff, anyhow? /
> \ _______,--------------' Chris Trask / N7ZWY
> _ |/ Principal Engineer
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> (__)\ _ P.O. Box 25240
> \ \ .' `. Tempe, Arizona 85285-5240
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> \ '" \ IEEE Senior Member #40274515
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> ------------------------------------
>
I used a thick piece of steel to avoid uneven heating and distortion
while clamping. When I heat the steel, my thermocouple (on the top
surface) lags the temp on the lower surface. So I heat the steel and
when the top surface is at the target temp, the bottom surface is at a
higher temp. Before I place the steel on the PCB/image sandwich and
after I remove it from the hot plate, I monitor the temp ... it will
continue to rise ... level out ... then begin to fall ... this is when
I place it on the sandwich (the large mass will maintain the temp
better after the sandwich starts to come up to temp) ...
I also place the PCB on about 4 plys of paper towel to help the self
leveling of the PCB ...
Steel will soften when heated and will buckle or flex while being
heated (steel is a poor conductor of heat) ... a thin plate with
heating elements close to the surface will show "a pattern" and cause
uneven heating ... using a thick sheet of steel between the waffle iron
surfaces will help but applying sufficient pressure will be difficult
... I also put a wooden handle on the steel block so I could handle the
steel without dropping it or burning my self!!
Practice, practice practice will eventually yield a good procedure
with your set-up ... or any other process ...
The good thing about the TT process is you can see the pattern on the
copper before etching and if it has defects, some acetone cleans it off
and you can try again ............
Jim KI6MZ
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