Complete Circuit Board Lab & POV Business Card

Step 3 Modify a Laminator

Be aware that the device you have modified is a now a potential fire and electrical hazard!  As such, you probably shouldn't leave it unattended. And make sure it's unplugged before you do any of this.

The Toner Transfer Process
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To create positive etch resist mask, the most straight-forward approach, with components readily and cheaply available, is known as the Toner Transfer method. The basic idea is that you print out your design onto a glossy paper and apply the printout to your board with heat and pressure. The paper is removed, leaving only the toner as an etch resist, thereby protecting the copper below from the acid bath.

There are a lot of variables involved, so it is easy to see why a lot of people give up on it. Given enough time, though, it is very possible to get the process dead on. If you have tried and given up on this method before, I'd recommend that you don't give up! The payoff in time and money saved is well worth it.

The process can also be used to add a black component label or text mask to the board, as a final touch after the copper traces are cleaned off. For the POV Card, I used this method to add my name to the back of the card in case the LEDs were too hard to read.

Modifying the Laminator
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The most important part of the process is a balance between heat and pressure that is consistent over the entire board. Proper pressure is easily achieved with a standard bag laminator. You just need to be sure to find one with heated rollers or you won't get the same results. GBC makes two commonly available models, the GBC Creative and the GBC Personal; they are functionally identical, except that the Personal has an extra switch.  

Now all we need is to get the temperature right. Since both of the laminators I mentioned are controlled by a simple thermal switch, all we have to do is swap it out with a higher temperature rating. It's pretty simple; the switch contacts open when the rollers are too hot, turning off the heaters, and close when it's too cold, turning it back on.  It's a very simple kind of hysteresis, where the heater is never exactly the right temperature as it is almost always slightly above or below the proper temperature, maintaining a +/- of about 7 degrees. It is very unlike the Watlow PID temperature controller I use later on in the reflow oven, which learns about the system and compensates dynamically.

Instead of a fixed value switch, you want try and find a variable thermal switch. Just like a fixed value thermal switch, it uses a bimetallic strip that warps with the changes in temperature. The two metals have two different coefficients of thermal expansion, and the whole piece bends forward at the proper temperature to close the contact.  Unlike a fixed value switch, however, it has a screw that can be adjusted, changing the tension on the bimetallic strip, and thus changing the distance it has to travel to close the contact and turn on the heater. It's all very clever and simple and perfect for our laminator; we can calibrate it to our hearts desire, even to the point of matching it to the melting point of the toner from the specific model of printer we use. Huzzah!

If you can't find an adjustable switch, don't worry; a 160-190º C fixed value switch will work just fine.

For safety's sake, we will have to swap out the low temperature thermal fuse (as opposed to bypassing it entirely. Definitely not recommended!) with one of a higher rating, so the whole unit will lose power if it overheats and hopefully doesn't catch fire. BTW, you do this mod at your own risk, so don't leave it on unsupervised! It's kinda dangerous. At its new temperature it may fume a little bit initially as gets worn in, but anything more means it's melting and you need to turn the temperature down. :)

My laminator is set to around 180º C (356º F). It varies +/- about 10 degrees, tested with a handy thermocouple directly on the rollers, taking care, of course, not to let the probe get pulled into the laminator. The fuse is for 240º C, for a good safe margin.

Parts

• GBC Creative/Personal Laminator
• Variable temperature thermal switch, ranged between roughly 100-200º C
• Crimp-on butt connectors
• Crimp-on screw terminal connectors, with appropriate sized miniature screw/nut
• 240º C thermal fuse

Tools & Supplies

• Wire strippers
• Crimping tool
• #2 Phillips Screwdriver
• Temperature probe