Etching double-sided PCBs

Hi Guys, lately I'm doing a lot of pcb etching, well, mostly prototype boards and small projects but until yesterday I was etching only single sided pcbs.

The past week I did a new project and I had to go double-side.
I did the layout, printed it then I sticked the layout together and I placed the board between the layouts.
I removed the "tape" on both sides of the board and I exposed it (I own a simple UV machine so I had to expose one side then the other)

Now, it looks like there is something wrong, and I don't know if it happens during the exposition or the development but, when i etch the board, one of the sides is ok, and the other is left almost untouched even leaving the board inside the etching solution for more than 20 minutes.

Probably I do something wrong during the development (or the UV exposition) well, I don't know.

But maybe some of you have some tricks to get it right ???

Some help would be really appreciated...

You need to make a small "pocket" out of your two layout sides, with sides made from exactly the same thickness material as your pcb material, and just fitting the actual pcb - otherwise you won't get proper layout/pcb contact. I use small strips of the actual pcb as spacers to acheive this.

Also, make sure your film layout is - on both sides - printed so that printing/ink side goes to touch the pcb, not on the outside. This also means that you need to be careful not to scratch the film while inserting your raw pcb into the film "pocket".

Jakob E.

gyraf said:

You need to make a small "pocket" out of your two layout sides, with sides made from exactly the same thickness material as your pcb material, and just fitting the actual pcb - otherwise you won't get proper layout/pcb contact. I use small strips of the actual pcb as spacers to acheive this.

Click to expand...

Do you mean making a "frame" around the PCB from scrap pieces of PCB material? Is this to keep the transparency from bending at the edges?

gyraf said:

Also, make sure your film layout is - on both sides - printed so that printing/ink side goes to touch the pcb, not on the outside. This also means that you need to be careful not to scratch the film while inserting your raw pcb into the film "pocket".
Jakob E.

Click to expand...

This means you have to print it reversed, right?

yes and yes...

Jakob E.

Hi Gyraf, thank you for your reply.
This is exactly what I did !

But honestly now I think there is something wrong with the boards.
I did it 2 times, and in both cases i had one side perfectly etched and the other untouched by the etching solution.

Could it be possible ?

Yep that could very well be. Especially in Switzerland,
where it is not uncommon for the local electronics place
to actually sell a double sided board once in a blue moon.

Maybe check it by cutting two strips off the same
board and exposing opposing sides for the same
amout of time, then you'll know for sure if it's your
board.

Öbrigens bi über Wiahnacht weder zLiachtaschtaa,
falls Bock häsch kommer jo mol bsuacha und Züg luaga

Liabs Grüassle,

Lukas