Blurry PCBs

[Electronics4you]

Hi there,

After 10 years of making PCB's using my old trustworthy UV exposure unit, I decided to make a new one with tubes on both sides to avoid flipping the PCB when making a double sided one (yes, I know it was a bit old school).

I have tried different exposure times, but the final results come out all blurry. Nothing else but the exposure unit has changed, so clearly something is going on here. The toner of the film is placed against the bare PCB to avoid light from the sides and reflective film in the bottom of the unit creates a uniform light exposure.

Have anyone seen this issue before with blurry PCBs and what the causes may be? Could it be other things such as bad photoresist, over-/underexposure etc.?

Thanks

 

[jpanhalt]

A picture of your exposed and developed PCB both before etching and after etching would be helpful. I have been using the photo method since the late 1990's and have never had that problem. Did have some bad resist once, but that manifested itself as flaking of the resist.

I am assuming same photoresist brand, same etching solution, and same type of UV lamps and glass as before. Some glass cleaners have UV blocking agents in them so the glass looks clearer and non-reflective.

John

 

[picbits]

It sounds like the boards may not be laying totally flat in the exposure unit. Even half a mm of the transparency from the board can cause bad exposure.

Also make sure the printed side of the transparency is in contact with the board itself and double check exposure times.

 

[Electronics4you]

picbits : As I wrote in my first post, the toner side of the film is against the PCB

jpanhalt : I'll check the glass/cleaner specs

 

[jpanhalt]

A glass plate coated with the UV blocking/ant-glare stuff should look distinctly different when viewed from an angle with sunlight. If you can post a picture of a "blurry" pcb, that would be immensely helpful.

John

 

[Electronics4you]

The bad PCBs where immediately discarded after first try, but if the issue continues after second try, I'll post an image

 

[Electronics4you]

Problem solved: My electronics supplier provided me with a wrong light tube with a wavelength different from the photoresist specs.