Tuesday, March 29, 2011

I Need More Magic

I have been building HomeBrew PCBs via the Toner Transfer Method for a long time, as seen in previous posts. I am still trying to perfect my use of this method, where I can expect the same results each time.

There is sill some Magic to be learned.

Currently I am trying to perfect the alignment of the second side of a two sided HB PCB. I am trying circle Targets as common art for alignment guides. So far, I have had limited, and unpredictable success.

The lack of success is not that I can not align the circuit pads for each side, but how to repeatedly do it.

The current difficulty is; My Targets keep falling off of the PCB in the water soak bath, before they can be used.

In an attempt to do everything just right, I created another revision of my QRP QRSS Beacon, which is a two sided board of about 2 inches by 1 inch. The Targets that I am using are about 1/2 inch diameter placed around the edge of the board at random locations.

For this run, I was careful to clean the board as usual, and run it through the laminator several time as before (about 5). Normally, I run PCB and Transfer Paper sandwich inside of a small pocket made from a manilla folder. Successive passes are with the sandwich just setting on top of the folder pocket material, so that the Transfer Paper is in closer contact with the heated roller and the overall thickness is the same.

I have always had a problem getting good transfer results near the edge of the PCB material, and therefore have always provided a boarder of about 1/2 inch around the desired circuit art work. Now with my Targets in that boarder area, they are the art that is being lost.

I tried to get everything just right for this run. All was going well, until I was walking to the sink where warm water was waiting to dissolve the transfer paper release agent.

As I walked, I heard a "snap", from the PCB and Transfer Paper sandwich which I held in my hand. I could see the sandwich starting to separate at the edge. The "snap" that I heard was the targets releasing from the PCB material.

I think cooling and/or shrinkage of the PCB or Transfer Paper is the problem. From previous experiments, I was concerned that this might happen, so I let the sandwich cool naturally after the laminator. But, apperntly it cooled further as I walked to the sink.

As can be seen in the photo, the circuit art in the center of the board transfered perfectly, even with it's small 8/8 circuit traces. Only some of the Targets were lost, but this attempt was all about obtaining good targets.

Three Targets across the top, and portions of the lower targets were lost in the water bath, ghostly outline remains on the copper from where the Targets were previously attached.

I know from previous non-PCB experiments, moisture content has an effect on paper that is put through a laminator. Here in the Puget Sound area humidity levels are high and may be problem that needs to be understood and taken into consideration.

Now, what to do about this heating and shrinking problem, or how to avoid the bad results?

Maybe preheat the Transfer Paper to help stabilize it, by removing moisture?

Maybe moving the sandwich from the Laminator directly into Hot water bath? But I think the Toner has to cool a little before it can be disturbed.

I think if I was working on lager or a more conventional size circuits, all of this would not be a problem, maybe only very thin lines are susceptible to the problem.

I am still working on my HB Double Sided PCB Methods - but so far, the Magic still alludes me.


No comments:

Post a Comment