Greetings to all, I am a new member and I must say I am very impressed with the wide range of knowledge you all have. My experience with homemade PCB's is limited to single sided boards made using the photo-etch technique....there are many other techniques that I plan to try, but if I can help in any way, I will. I've recently moved from Chattanooga to Colorado Springs, so I haven't set up my circuit workshop, but I am thinking about a whole new approach. With that said:
>
> Second I am interested in through hole plating. I know there are various mechanical work arounds (panel pins, favorits, etc) but I would like to try and make a real through hole plating machine.
> I have some heated pressure rollers (they goto about 200 C) and have got a working control board for them. What I need to do is figure out how to melt solder and flow it over the board. My best idea is to get some of those ceramic heating elements (from hair tongs) and line a hopper with them, then use gravity to get the molten solder to flow onto the joint between the rollers, feed the board into that and catch the drip (and the board) on the other side. Has anybody tried this before?
I have not tried this, but I have thought about it a lot. My thinking was to use some sort of temporary solder mask(perhaps peel-able or regular) , mask off the entire PCB except where the via's would be, then dunk the entire board into molten solder, dunk into a solder pot like the 2000W unit sold by jameco.com (part# 149876), using some sort of ceramic tongs to hold the board. If this method worked you would be able to make through holes on PCB's whose dimensions would be less than 12" by 8"(a lot of circuit can fit that area).
My greatest curiosity to the above mentioned idea, is to how well would the joints hold up if one was to then reflow the board with components (I presume the surface tension of the solder would keep the joints sound...but only trials would prove the concept.)
>
> Lastly (for now) I want to build an SMT oven. Again inspired by a design in Elektor I think one would be possible, but I intent to cheat a bit as I will be using an very different oven, one made for pizza!
> It is thin and flat with massive heating elements both top and bottom. Do you think it will be better than the usual toaster oven?
>
With some basic temperature monitoring equipment you should be able to achieve good results, since there is an element on the top and bottom, you will get better heat dispersion, which will result in less thermal stress of the PCB itself.
I made a reflow oven out of an old black&decker toaster oven I found at a thrift store for $10. I completely gutted the electronics and only left the heater elements and the door switch. I developed a microcontroller circuit to handle the whole process. Instead of using a thermocouple like most people do (because I was getting a lot of noise in my previous TC amplifier circuit), I used a glass bead thermistor, made by Honeywell(this thermistor has such a wide range, it is safe and reliable for reflow solder work), in the back of the unit in the middle of the oven was a small hole where the thermistor entered the oven. I used a discrete control loop, basically the output control was an Omron SPST relay connecting the heating elements to 110V. For the micro I used an Atmel Atmega8 programmed in basic. As a simple setup I was really impressed with it, and it allowed me to easily mount SMT components on my single side PCB's, I was also able to get a free sample of solder paste from Manncorp, and considering the small amount of boards I was making, I was set.
One thing to consider when using a reflow oven, is the PCB material itself. I was able to use the oven with paper phenolic substrates as long as the substrate had minimal moisture. I found this out the hard way once, I had just finished etching and washing the board, then solderpasted the pads, placed the components, and popped it in the oven...during the preheat/soak period of the reflow profile the board started making a poping noise and cracked. I stopped the process and inspected the board, only to find where the moisture in the board started to expand and break the board itself.
Basically if you decide to reflow paper phenolic PCB's, make sure to let them dry out for a good long time before reflowing them.
Cheers,
Daniel