Expose one side first, then the other, and develop both of them together. Just make sure that both transparencies are aligned. Here's what I do: I attach the transparencies together (that's easy to do when there is no board between them), putting some sticky tape at the three of the four sides. Then slide the board between them and secure it with some tape at the fourth side. Note that the three first sides of the transparencies must be longer by at least one centimeter than the board. Careful not to scratch the printed (inner) sides of the transparencies as you slide the board in. Also, when you put the board in the developing container, make sure that the photosensitive material of the "down" side of the board is not scratched by the bottom of the container.
Above advice is good.
Re management of vias: I tend to limit the number of vias, then either or use resistor pads as vias (soldering the resistor / transistor / whatever top and bottom) or solder in tinned copper wire through the vias if I can't arrange for a convenient component lead to do the job.
Works pretty well as long as you are disciplined in the number and placement of vias.
I have not heard of anybody doing "home plated through holes" but I would be fascinated to hear if it can be done!
Re management of vias: I tend to limit the number of vias, then either or use resistor pads as vias (soldering the resistor / transistor / whatever top and bottom) or solder in tinned copper wire through the vias if I can't arrange for a convenient component lead to do the job.
Works pretty well as long as you are disciplined in the number and placement of vias.
I have not heard of anybody doing "home plated through holes" but I would be fascinated to hear if it can be done!
I do both sides separately.
Leave the mask on the one side until the first side is etched.
Drill the four corner holes and use them to key both sides together.
Mask the finished side with masking tape and carry on with the second side.
If you leave a few mm around the edge of the board you wont get any bleeding along the edges of the masking.
Getting the exposure right can be a bit frustrating. My laser printer doesn't produce a completely opaque image so I often print two copies and layer them.
Leave the mask on the one side until the first side is etched.
Drill the four corner holes and use them to key both sides together.
Mask the finished side with masking tape and carry on with the second side.
If you leave a few mm around the edge of the board you wont get any bleeding along the edges of the masking.
Getting the exposure right can be a bit frustrating. My laser printer doesn't produce a completely opaque image so I often print two copies and layer them.
I am slightly lost, why do we need to do the sides separately? I have not done it yet, but my idea would be :
1) print two transparencies
2) somehow affix them on the two sided PCB and make sure they align
3) expose in UV light
4) develop in photo resist liquid thingy
5) wash with water
6) dip in acid to remove copper
7) wash in water
8) dip in tin/silver solution if wanted
9) wash
10) drill
1) print two transparencies
2) somehow affix them on the two sided PCB and make sure they align
3) expose in UV light
4) develop in photo resist liquid thingy
5) wash with water
6) dip in acid to remove copper
7) wash in water
8) dip in tin/silver solution if wanted
9) wash
10) drill
Just cos its easier. It's awkard to get both sides perfectly aligned otherwise.
There are of course many ways to align both sides - you will find out which method suits you in time.
The above process looks very easy but believe me when I say it doesn't always go according to plan.
There are of course many ways to align both sides - you will find out which method suits you in time.
The above process looks very easy but believe me when I say it doesn't always go according to plan.
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If I use the "press and peel" process I do each side seperately as Katieanddad does. While I have not used photoresist for a while (mainly because I seem to have got on top of the press and peel process) when doing boards photographically I do both at the same time.
Tricks to watch for are:
- Protecting the PCB surface while etching (the bottom side can be scratched) I drill and mount nylon bolts in the PCB to ensure it does not actually touch the bottom of my etching dish.
- Getting the plots properly aligned is not trivial. Not the least because laser printers are NOT lab instruments, and you find distortion across large images. This seems to be fairly constant from print to print, but you need to watch out when doing double sided PCB's because when you flip the plots for the "other side" I usually find that there is some mis-registration across larger boards.
Tricks to watch for are:
- Protecting the PCB surface while etching (the bottom side can be scratched) I drill and mount nylon bolts in the PCB to ensure it does not actually touch the bottom of my etching dish.
- Getting the plots properly aligned is not trivial. Not the least because laser printers are NOT lab instruments, and you find distortion across large images. This seems to be fairly constant from print to print, but you need to watch out when doing double sided PCB's because when you flip the plots for the "other side" I usually find that there is some mis-registration across larger boards.
If you are printing from a laser or inkjet, use the heaviest weight transparency sheets you can, they are more stable and always print the image so the print side will be against the PCB to be exposed (emulsion side down), this will give the best image on your PCB. If you do a few PCBs of a regular size make yourself a jig. professional PCB fabricators work by having standard panel sizes (12" x 18" is common) and have tooling holes and alignment marks around the outside of their working panel, these correspond to jigs and carriers that hold the blank PCB and artworks.
For smaller boards use your mounting holes, for registration always use a minimum of 3 holes.
One printing pass is best, up the contrast and darkness to get the darkest image, then inspect your artworks on a light box using some paint to cover any pin holes or defects and a blade or eraser to clear any unintentional blobs. Printing twice never lands in the same place exactly leading to ghosting on the edges, you want a clear defined edge.
For smaller boards use your mounting holes, for registration always use a minimum of 3 holes.
One printing pass is best, up the contrast and darkness to get the darkest image, then inspect your artworks on a light box using some paint to cover any pin holes or defects and a blade or eraser to clear any unintentional blobs. Printing twice never lands in the same place exactly leading to ghosting on the edges, you want a clear defined edge.
I'm assuming that you haven't made DIY boards using this process:-
DO, DO, DO a test piece. Using a small piece of board, test your exposure, every UV tube and board will be slightly different.
Once exposed you can't go back, the aerosol cans of photo resist are a poor substitute for pre-treated boards.
DO, DO, DO a test piece. Using a small piece of board, test your exposure, every UV tube and board will be slightly different.
Once exposed you can't go back, the aerosol cans of photo resist are a poor substitute for pre-treated boards.
When you get your light box make a dummy run with pretreated boards. Take a 10cm long piece and expose at one minute each cm by sliding an opaque material out every minute. After developing and etching you will then have your exposure time for that box and brand of board.
For double sided you can make a very easy jig out of another piece of scrap board of the same thickness in the shape of a woodworking square, 90° L shape. Tape your two transparencies together at one corner only i.e. top/right, cutting one transparency slightly smaller than the other well help. Slide your jig under the bottom/left corner and tape down, tape at the other corner will keep it perfectly aligned. You can then remove the top/right tape. When you slide your board into the 90° angle, tape it down tightly onto onto the jig so you can handle it safely. You can now tape down your duplicate prints if you need it. If your prints are not so good, a once over with a white board marker will help. It adheres to the printed areas but wipes off the other. When you expose both sides one after the other, put a brick on top for a nice flat exposure. It will also help if you have a nice easy off tape. I use "invisible tape". Flux your board if not being use immediately. I have an awesome cheap homemade flux that works great. Shout if you want the recipe.
For double sided you can make a very easy jig out of another piece of scrap board of the same thickness in the shape of a woodworking square, 90° L shape. Tape your two transparencies together at one corner only i.e. top/right, cutting one transparency slightly smaller than the other well help. Slide your jig under the bottom/left corner and tape down, tape at the other corner will keep it perfectly aligned. You can then remove the top/right tape. When you slide your board into the 90° angle, tape it down tightly onto onto the jig so you can handle it safely. You can now tape down your duplicate prints if you need it. If your prints are not so good, a once over with a white board marker will help. It adheres to the printed areas but wipes off the other. When you expose both sides one after the other, put a brick on top for a nice flat exposure. It will also help if you have a nice easy off tape. I use "invisible tape". Flux your board if not being use immediately. I have an awesome cheap homemade flux that works great. Shout if you want the recipe.
When you get your light box make a dummy run with pretreated boards. Take a 10cm long piece and expose at one minute each cm by sliding an opaque material out every minute. After developing and etching you will then have your exposure time for that box and brand of board.
For double sided you can make a very easy jig out of another piece of scrap board of the same thickness in the shape of a woodworking square, 90° L shape. Tape your two transparencies together at one corner only i.e. top/right, cutting one transparency slightly smaller than the other well help. Slide your jig under the bottom/left corner and tape down, tape at the other corner will keep it perfectly aligned. You can then remove the top/right tape. When you slide your board into the 90° angle, tape it down tightly onto onto the jig so you can handle it safely. You can now tape down your duplicate prints if you need it. If your prints are not so good, a once over with a white board marker will help. It adheres to the printed areas but wipes off the other. When you expose both sides one after the other, put a brick on top for a nice flat exposure. It will also help if you have a nice easy off tape. I use "invisible tape". Flux your board if not being use immediately. I have an awesome cheap homemade flux that works great. Shout if you want the recipe.
For double sided you can make a very easy jig out of another piece of scrap board of the same thickness in the shape of a woodworking square, 90° L shape. Tape your two transparencies together at one corner only i.e. top/right, cutting one transparency slightly smaller than the other well help. Slide your jig under the bottom/left corner and tape down, tape at the other corner will keep it perfectly aligned. You can then remove the top/right tape. When you slide your board into the 90° angle, tape it down tightly onto onto the jig so you can handle it safely. You can now tape down your duplicate prints if you need it. If your prints are not so good, a once over with a white board marker will help. It adheres to the printed areas but wipes off the other. When you expose both sides one after the other, put a brick on top for a nice flat exposure. It will also help if you have a nice easy off tape. I use "invisible tape". Flux your board if not being use immediately. I have an awesome cheap homemade flux that works great. Shout if you want the recipe.
Developing and etching each side separately may or may not work - depending on how accurately you manage to seal the side not in the process.
I've been making prototype and smll series PCBs for almost 40 years with slightly different processes. If you want to process both sides simultaneously, you need to fix both sides of the artwork to the raw PCB, so that it doesn't move in the process. I usually make an envelope of the films, and tape the envelope to a slightly oversized raw PCB. If your new light box is single sided, you need to make sure that stray light does not fing the other side. Also - if you etch one side at the time, make sure to properly seal the side not in process.
Do make a test strip at appx 30 sec intervals, to get a feel for the intensity of the light source. BTW - which light source do you have? The rather common version with 8 15W tubes for each side usually gives appx 2m30sec per side....
You mention special foils for laser printer - If these are LaserStar foils, they are good - I've used them for 20years+++
I've been making prototype and smll series PCBs for almost 40 years with slightly different processes. If you want to process both sides simultaneously, you need to fix both sides of the artwork to the raw PCB, so that it doesn't move in the process. I usually make an envelope of the films, and tape the envelope to a slightly oversized raw PCB. If your new light box is single sided, you need to make sure that stray light does not fing the other side. Also - if you etch one side at the time, make sure to properly seal the side not in process.
Do make a test strip at appx 30 sec intervals, to get a feel for the intensity of the light source. BTW - which light source do you have? The rather common version with 8 15W tubes for each side usually gives appx 2m30sec per side....
You mention special foils for laser printer - If these are LaserStar foils, they are good - I've used them for 20years+++
I've made hundreds of boards as you describe. For alignment I make my overall layout 1" larger on all sides and put a target or moire on all four corners. this looks like a gun sight scope's cross hairs or a ringed target. Align both transparencies and secure with tape across one end so that they can open and close like a book. tape this sandwich on the on the opposite side bottom transparency side to the glass frame. Put the PC board onto the opened transparency and tape it's corners to the bottom transparency. Fold over the transparency top, be certain that the moires are perfectly aligned. I use a loupe to check, then tape the other corners to the bottom glass. I now put the top glass on the entire conglomeration and secure with wing nuts. I used to expose each side at a time but now do both simultaneously.
I should explain that I made my exposure frame and exposure setup from materials lying about the house. If you are going to expose in an open frame as I do in the basement, block most sunlight. It's not necessary to go crazy and have the room totally dark.
You can not do thru hole plating at home without the addition of expensive equipment. you need to remember to solder the lead to both sides of the board, or in the case of radial components mounted on the top with the ground plane on top, design the board with a hole near the bottom of one lead that clears the footprint of the component then bend the lead and pass it from bottom to top and solder the top. If the leads are small an extender trace on the bottom that clears the footprint of the component can be soldered from bottom to top using a cut off lead from other components. I always keep a supply of various thickness scrap copper leads for this purpose.
I should explain that I made my exposure frame and exposure setup from materials lying about the house. If you are going to expose in an open frame as I do in the basement, block most sunlight. It's not necessary to go crazy and have the room totally dark.
You can not do thru hole plating at home without the addition of expensive equipment. you need to remember to solder the lead to both sides of the board, or in the case of radial components mounted on the top with the ground plane on top, design the board with a hole near the bottom of one lead that clears the footprint of the component then bend the lead and pass it from bottom to top and solder the top. If the leads are small an extender trace on the bottom that clears the footprint of the component can be soldered from bottom to top using a cut off lead from other components. I always keep a supply of various thickness scrap copper leads for this purpose.
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