Problems exposing/developing a Bungard PCB

[akis]

I have tried to use a two sided Bungard FR4 PCB. I have tried various exposure times, from my normal 5.5mins to 9 mins. Then during development I have checked to see that the traces are all visible. But the dye of the resist is a copper colour and very hard to see the difference between properly developed and not - the traces are clearly visible but it is not clear if the exposed areas have been properly removed. During etching it just does not seem to work implying either under exposure or underdevelopemt. I typically use the Mega laminates and they work perfectly under same conditions. I just thought I would try the Bungard for better quality but I am finding it impossible to work with. Any suggestions?

[Fred27]

I've had no problems with the Bungard boards. I use a metasilicate based developer. My exposure time is about 4 minutes using a cheap eBay nail lamp. Maybe you're over exposing?

When doing an exposure test, I like to have one piece where I completely removed the resist with acetone, one that has had 10 minutes with no transparency and one that was completely covered. That should let you know exactly how an exposed and unexposed area react. It helps make down problem to the exposure or the development.

[128er]

I've had no problems with the Bungard boards. I use a metasilicate based developer. My exposure time is about 4 minutes using a cheap eBay nail lamp. Maybe you're over exposing?

Yes, same thing for me. 4 minutes exposure time with ebay nail lamp. I use sodium hydroxide (NaOH) for development.

I once used another brand than bungard - man, that was crap . The photoresist was total uneven. However...

How does your board look like after development? In most cases you can already see at this step if your results became good or not. The traces should be clearly visible with a rather good contrast after development .

But the dye of the resist is a copper colour and very hard to see the difference between properly developed and not

For me that sounds clearly like over-, or underexposed, if the contrast after development is not clearly visible.

What type of lamp do you use for exposing? With UV lamps I never had to expose more than 4 minutes. But your 5,5-9 minutes sounds quite long.

[akis]

After development I can see good contrast. But the colours are red-orange and.. red-orange. It is like trying to compare two shades of the same colour. I suspect that the exposed areas where the photo-resist ought to be removed, are not well exposed or the developer has not managed to remove the resist properly. But as the resist and the copper cladding are the same colour, it is hard to tell.

[128er]

Hmm, sounds strange. Somewhere in your process chain is an issue. From my remembrance, the exposed parts should look like the red-orange/copper as you described. The rest should be more like a pale dark purple.

I have no idea at the moment. Show us your exposure mask. Describe your process step by step. Did you do something different now, than at your previous PCBs?

 

[akis]

I made another PCB 5 minutes before the Bungard! Same lab, same UV unit, same chemicals.

I believe the problem is with the development process sounds like under-development. I made another board and developed it for far longer even though you cannot tell just by looking at it if it is 10 seconds or 100 seconds over-developed. The etching process will show, will etch it later and will report back.