Double-Sided PCB Alignment

[grempel1]

Hi,

I am looking for advice on a successful method for aligning the circuit patterns/images on double-sided PCBs.

There must be a simple way of doing it but so far it has eluded me.

Thanks.

Rgds,
Gary

[Chippie]

how about having alignment marks on your layouts that are printed onto your transparencies ?

[simingx]

What I do is cut the PCB exactly to size, then making sure your artwork has alignment marks as well, place the film exactly over the board. Works pretty well most of the time... Another way (not tried) is to stick the 2 films together and sandwich the board in between, but then you need a light box capable of exposing both sides at a go.

[Comatose]

What I do is drill some of the holes first, before peeling off the backing on the presensitized board. 4 nicely spaced ones should do it.

Print one copy of your artwork for one side onto normal paper, then sprayment that onto the peel layer of the PCB. Drill a few marker holes. Line up the artwork with the holes when you expose it. viola!

[Chippie]

What I do is cut the PCB exactly to size, then making sure your artwork has alignment marks as well, place the film exactly over the board. Works pretty well most of the time... Another way (not tried) is to stick the 2 films together and sandwich the board in between, but then you need a light box capable of exposing both sides at a go.


Simingx, why do you need to expose both sides simultaneously? ;) Surely one side can be exposed then turn over and process the other?

I've sat and often wondered the best way to process double sided boards......havent tried it because I dont have any DS board..........lol :D

Some good ideas here tho' ;)

[zagisrule!]

I process one side first, then drill a few holes to use as alignment keys when I process the other side.

Once both sides are processed and look good I go ahead and etch.

I wish there was a way to make thru-holes at home! Bent wires don't really do the trick like the real deal as far as vias are concerned. Another tough one is putting a trace on the top and bottom layer for a radial electrolytic, hard to solder two sides and maintain a good appearance.



-Matt

[simingx]

Simingx, why do you need to expose both sides simultaneously? ;) Surely one side can be exposed then turn over and process the other?

I've sat and often wondered the best way to process double sided boards......havent tried it because I dont have any DS board..........lol :D

Some good ideas here tho' ;)

To prevent the board from moving when you're turning it around.... :D
But, making double sided boards at home also involves a certain amount of luck... :o

[ZAGNUT]

I wish there was a way to make thru-holes at home! Bent wires don't really do the trick like the real deal as far as vias are concerned. Another tough one is putting a trace on the top and bottom layer for a radial electrolytic, hard to solder two sides and maintain a good appearance.



-Matt

seems like i remember seeing small eyelets that are placed in the drilled hole and then rolled or punched to make contact with both sides of the board.


dave

[Chippie]

To prevent the board from moving when you're turning it around.... :D
But, making double sided boards at home also involves a certain amount of luck... :o


....but isnt that the point of having datum marks/alignments points.......? :D

Actually I never considered that the board would move.

I s'pose one could use a double sided adhesive tape to secure both transparencies, assuming the board is cut over size........

nice to know that someone can state the obvious when it is missed........cheers Sim. ;)

[zagisrule!]

seems like i remember seeing small eyelets that are placed in the drilled hole and then rolled or punched to make contact with both sides of the board.


dave

I remember seeing these too. I think they are used to repair broken or damaged vias. I don't see any reason why we could not use them as vias right off the bat. I am going to check into costs.

Good thinking man, this might just make it possible!



-Matt

[grempel1]

Thanks for the suggestions on alignment.

Two other questions.

1. What is the best or most effective way of cutting pcb material into smaller pieces while doing least damage?

2. What size or sizes of drill bits are used when drilling the pcb?

Thanks for your advice.

Regards,
Gary

[simingx]

1) Fast: Circular table saw, Slow: Hacksaw.
2) I usually use 0.8mm for ICs, resistors, capacitors etc, and 1.0mm for other things like diodes, voltage regulators and larger transistors. You may occasionally need a 1.2mm hole for large rectifiers etc.

If you have a drill stand, by all means spend the money and get carbide bits (for at least the 0.8mm size), as glass fiber boards will eat HSS bits for breakfast, lunch and dinner.. :D :eek:

[Comatose]

You can also use large metal cutting shears (not aviation snips) to cut PCBs to fairly good effect if you're without a table saw (or bandsaw, or miter saw, or hell just about any saw works)

A $30 jigsaw works well too.

[Chippie]

I recently had to make 25 pcb's for some lost model alarms......size: 25mm by 12mm........pretty small to work with.

I copied the track layout onto acetate sheet so that the layouts fit onto a 6inch * 4inch pcb.
I processed the boards in the normal way, then I drilled them..tedious! then cut them with a band saw, and sanded them to right size with a disc sander....a somewhat labour intensive job I know but at least I get the job done........thats my way until I find a better way for pcb production small scale or mass production.. ;)