Are these the right UV tubes for pcb dry film photoresist exposure ?

[BravoV]

Bought these at local brick & mortar approx. $ 1.5/pcs, are these suitable for the job ?

Also I made a thread asking how to power these -> Here

[Balaur]

Those look like "BLB" (i.e. blacklight/night clubs) with wavelength peaks at 350-370nm.

Most pre-coated PCBs have a good response for a 350-450nm spectrum. While "white" UV tubes or LEDs are recommended, your tubes may work.

You will have to do some trial runs of course, not only to account for the tube characteristics but also to cover the specifics of your box/toner/film, etc:
- build your UV exposure box
- print a testing pattern consisting in several traces of variable length
- cut several pieces of PCB
- expose them individually while protected by the test foil for a few reasonable intervals of time
- do finer tests around the best performing combination

While you are certainly perfectly aware of all this, and with the risk of appearing pedantic, I would really like say that it's important to have a repeatable procedure to minimize later disappointing and loss of materials.

The procedure is a combination of:
- quality pre-coated PCB material. I had significant issues with that and it's better to find something that works good and stay with that
- uniformity of UV exposure
- good media
- correct UV exposure duration
- quality developer (i.e. not sodium hydroxide) and developing time


Mike's site it's a very good reading.

Best regards,
Dan

[carloscuev]

If you're into dry-film, basically we only can get thru ebay 2 types of dry film:

Dupont Riston Series Dry-Film: (http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/datasheets/mm500series.pdf)
eBay: http://www.ebay.com/itm/171012338332

Hitachi Chemical Dry-Film: (http://www.hitachi-chem.co.jp/english/products/pm/)
eBay: http://www.ebay.com/itm/390414280019

And AFAIK they both work best with 365nm which is arguably the center of the UVA range.

I was going to make a black light tube box, but then I stumbled upon this 11Watt 365nm LED from LEDENGIN: http://www.ledengin.com/files/products/LZ4/LZ4-00U600.pdf its $99.88 USD in Mouser-USA, however it costed me $127.24 USD from Mouser-Mexico (I also recommend buying this Ohmite brand heatsink: SA-LED-176E and this LEDENGIN brand lens: LLNF-1T06-H) and it works very good, the light output is parallel so you have sharper exposure, practically that means it's easier to achieve thin traces

[BravoV]

Dan, thanks for the long & detail reply, really appreciate it. 

Missed that Mike's site, apparently these BLB are not the best, have to admit I didn't do much reading & research 1st before buying those tubes, it was a spontaneous buy cause they're so dirt cheap. All my pcbs were made using laser toner transfer method, this UV photoresist is new to me and planning to use the film instead of pre-coated pcb.

I will definitely do trial runs at small pieces 1st, and I guess a it over exposed wont hurt to if the tubes is emitting the right wavelength.

Now, next step is finding the suitable exposure box as Mike suggests or make one. 



@carloscuev,

Thanks for pointing out the uv led, unfortunately I'm just a hobbyist and that led you suggested is not justifiable, I will try these tubes 1st and see how they perform.

Btw, looking at different types of these photoresist films, the one I have is blue color, I guess its made by Hitachi, while the Dupont's is green.

Any experience that you could share on both ? Which one is better ?

[poorchava]

Look at auction sites for manicure uv lamps. They usually contain either one or four 9W tubes. Those emit mostly in 360-385nm range, which seems to be perfect for this application (and they are cheap as hell - I bought from mine from auction used for something like $5.5 )

[BravoV]

Manicure lamp  , never thought about it. As the best is the insect lamp as Mike's info, now I know what to find should these BLB failed miserably and I can't source insect lamp easily here,  thanks for the hint. 

[BravoV]

Found insect fl tube,  this should be the right one and also noticed there is a word "BL368" printed at the tube's label, I guess that stands for "B"lue  or "B"lack "L"ight at 368nm wavelength. 

[Thor-Arne]

I've also started looking into dry film photoresist, I've bought this one to test a little.

I was thinking of modding a scanner into a UV exposure box, but I'm not quite there yet.

I've tested regular fluorescent tubes and UV led's so far, and plan to test those insect tubes too before staring any modding. Another idea might be to use tubes for those face solariums.

So far I've figured a exposure time of 30 minutes for regular fluorescent and 5 minutes for UV led's.

[BravoV]

I didn't know ordinary FL lamp works too, even not as good as uv lamp. 

Btw, have you found alternative source to buy those photosensitive film for solder mask ? Cause even on ebay, currently the suppliers are originated only from Europe, have to find alternative cheaper source cause s/h cost is quite high from there.

[SeanB]

For one UV eraser I use a mercury vapour arc tube, just built it a high voltage current limited supply ( 2 transformers back to back of 3VA rating) and it worked quite well. Arc was not really arc, more a very bright glow discharge. Was very effective as you could do one chip at a time, and erase in around 10 minutes. Was small as well, fitted into a plastic slide out drawer used to hold components. Slide out, place chip in foam and close then turn on.

[sleemanj]

I've been using negative dry film for a bit.

I have exposed with both an array of UV LEDs, and the good old sun.  Frankly, the sun works just fine and saves soldering a hundred LEDs... but the UV box is handy for when it's dark out :-)

For hobby usage, there is miles of "wiggle room" in your exposure times, as long as your artwork is dark enough (print two copies on tracing paper, put them together, and make sure they are printed so that toner-side can be against the board).

The hardest part about using dry film, is getting it on the board.  For that, use a laminator and a carrier, it's just much easier than trying other methods. 

Have attached a document I wrote with my tips-n-tricks (don't worry, I sell small quantities of stuff here in NZ to hobbiests, I didn't write it especially for you ;-)).

[BravoV]

sleemanj, wow, thank you very much for that writing, there are tons useful and valuable tips & knowledges in there, really appreciate it. 

No doubt after reading your writing there, you must be very experienced on this work, now questions :

- Regarding the top & bottom sides, what happened on the result if you put it up side down ? Have you ever tried it ?

- From internet I saw there are two different types based on the film colors, which are blue and green, whats yours ? Mine is blue and wondering if there are significant different.

- What happened if you over exposed them by big margin ? Is it better to have it slightly over exposed rather than slightly under exposed ? My concern is how bad on the final result caused by overexposure at the uv bleed effect between two traces that are placed tightly together, say like QFP pins.

- About the wet lamination method, since its logical you can not just squeeze out 100% water residue underneath it, just curious if it will cause any problem especially formed and trapped bubbles when the pcb is heated, say like run it through hot laminator ? For sure the trapped water will evaporate somehow.

- How about the photoresist film for solder mask ? Any experience and tips ?


Yeah, lots of questions  , hope you don't mind.

[sleemanj]

I am far from an expert.

I don't know if it will work "upside down", but it doesn't really matter since the film on the bottom side is always the one that pulls away, it is bonded less strongly than the top side one.  So even in the unlikely event your piece is totally curl-less, just do the tape on both sides of a corner and pull-apart trick, the bottom side will pull off, the top side won't.  If you do have a curl, the bottom is always the inside of the curl.

I am using the typical blue stuff you can get on ebay (a poster above indicates this is hitachi, I have no idea, it's the anonymous blue stuff bought from Chna).

It's hard to over-expose as long as your artwork is dark enough.  Overexposure could especially lead to widening of the traces and some "blurryness" around the edges of traces (UV creeping under the edges).  Underexposure could lead to the traces not sticking of course.  But there is a large amount of tolerance (for amateur usage),  I've done spacing down to 8mil under sunlight with tracing paper and an (untimed) exposure about 10 minutes in full sun, after developing I carefully inspected the board and only in a couple of places did I have to use the tip of a pin to make sure there was no resist bridging those 8 mil gaps before etch, I may not even have needed to but far easier to clean up the resist with a pin than to cut bridged copper.  I think you'd be able to do most QFP without any trouble at all.

With wet-lam, I've only tried it once, so can't really comment, but I think as long as you use a laminator or a squeegee firm enough, all the water will be pressed out.

Not used it as soldermask, but I believe others have with success.

[BravoV]

Thank you very much, thats exactly what I expected to hear about the exposure.