Homebrew PCBs

Hello Mark,
                  For the want of a simple answer :(

NORMAL fuser temperatures range from about 160^C to about 200^C. Some even 
venture outside this.

In reality it is not temperature that is important but (mili) watts per 
pixel. If you imagine the toner to be a bitmap then each pixel requires the 
same power. More pixel's means higher power. Thicker paper means more power. 
However the pixel's are normally more important than paper thickness.

Modern fusers are predictive. The CPU knows how many pixel's are across the 
(each) next line coming to the fuser and how slowly the fuser heats due to 
its thermal mass so it can correct for this by increasing the supply power 
timed in advance to provide the optimum power at the correct time.

Older hot roller fusers had too much thermal mass for such predictive 
calculations to have any effect. These at a guess would have been in the 
rang 165^C to 195^C.

Copper boards however are a different story as copper is one of the best 
thermal conductors. This introduces other considerations.

One approach is to use a higher temperature and a higher feed rate so that 
the toner dissipates most of the energy before it can transfer (in lager 
quantities as temperature) to the copper laminate. A slower feed will have 
the effect of preheating the toner before it gets to the heater roller which 
in turn causes a higher temperature when it does get there. Ironically a 
smaller heater roller that has a lower thermal mass, will loose temperature 
before getting to the preheated toner cancelling some or all of this effect. 
Keep in mind that a heat roller rotates several times over one print.

Another approach is to use an oven in which case it is best to preheat the 
oven to just below the liquid/soft plastic state of the toner. After some 
time it can be considered the thermal mass of the laminate has evened out 
with the toner. You could then increase the temperature at a set power rate 
and time the process or complete the process at a fixed temperature. On a 
lower powered oven it may be necessary to raise the temperature to a fixed 
maximum and leave it there for a fixed time.

I would pre heat an oven to about 120^C to 130^C and then place the board 
into it for 15 minutes or so. Then increase the temperature control to about 
165^C to 170^C and watch the toner carefully. A minute or so after the toner 
appears more glossy I would remove it. Some toners may not have the glossy 
property so it would need to be timed. The most critical issue is the 
maximum temperature. There is a temperature rage within which the toner 
melts slowly. The lower the temperature you can get it to do this, the 
better as timing then becomes less critical. The copper has a high thermal 
mass so if it is over heated it will stay to hot for a while. So if the 
toner gets to close to melting point then the toner pattern will most likely 
be ruined.

Thanks Rob.

----- Original Message ----- 
From: Mark

As for laminators, I just bought a Staples machine - no adjustments. I also 
just ordered a pid temperature controller that I will use either with the 
laminator or with a "hot plate". Does anyone know the proper fuser 
temperature??

BTW, I'm not sure whether registration for double sided boards will work - 
it would require a precision optical sensor plus a rigid mechanical guide. 
The simplest way is probably to use two single sided boards of half the 
thiskness and use registration pins for alignment, then glue them together. 
Should work fine.

Mark
---------------------------