On 25/03/2011 07:18, Vitaliy wrote:
> Oli Glaser wrote:
>> Yep, pretty easy as long as the hole is drilled right. They give you a
>> drill size (0.2mm larger IIRC) for each corresponding rivet e.g. 0.4mm
>> rivet hole size needs 0.6mm drill bit, 0.6mm rivet needs 0.8mm bit and
>> so on.
> Thanks! We'll definitely get the rivets but will skip the punch.
>
>
>>> What is the advantage of using UV over presensitized PCBs sensitive to
>>> regular light?
>> I'm not sure, never used sunlight. I imagine the timing is more
>> repeatable (3-4mins for our UV box) as the strength is consistent, so
>> maybe there is less risk of over/under exposure. Possibly the focus of
>> sunlight is better given it's a direct point far away, though as long as
>> the mask is flat (no space underneath for "sideways" light to get in)
>> then this shouldn't matter much - the more expensive UV boxes have
>> vacuums to hold the mask flat.
> I never said "sunlight". :) We use a 64W CFL lamp, though in the past I u=
sed
> 100W incandescents. We use these PCBs:
>
> http://www.mgchemicals.com/products/600.html
>
>

Ahh, I should have realised that - that makes better sense :-)
To answer the question again, I think there is probably little=20
difference. Interestingly, the wattage levels for  CFL and UV tubes to=20
get the required levels look around the same (64W as opposed to=20
4x15=3D60W, both take around 3-4 min)
I would have expected you to need higher wattage as CFL is not a=20
"dedicated" UV source.

>> How long does it take to expose your boards using sunlight?
> Regular light (see above): about the same as your UV boards (3-4 minutes)=
..
>
> See this video for the basic process:
>
> http://www.youtube.com/watch?v=3D_sdcucoWj4E&feature=3Dplayer_embedded#at=
=3D62
>
> A few notes on the video:
>
> - You really shouldn't take off the black plastic with the room lights on=
..
> We use a yellow bug light in our "dark room".

Good idea - we just turn the main light off when taking the plastic off=20
at the moment, the board then goes straight into the UV box.

> - He says exposure takes 10 minutes, but with our super-bright CFL we cut
> the time in half.
> - Etching does not take 30 minutes (assuming the solution is already
> preheated). IIRC it only takes about 10.

I watched the video - just in case you weren't aware, one thing I found=20
out about Ammonium Persulphate which he also mentions there is that it=20
takes longer to etch; longer etch times mean (as you probably know) more=20
undercut and less accuracy (he mentions that FeCl is better normally,=20
the Ammonium Persulphate being used for demo purposes as it's clearer)

> - We figured that printer toner is cheaper than etchant, so we use genero=
us
> copper pours in Eagle.
> - We leave the green resist on, after etching. It can be soldered through
> very easily, protects the copper from oxidation, and looks cool.

Will have to try that - I read that some of the resists can be left on=20
and have a protective flux effect, so I guess it makes good sense.

> - Double-sided PCBs are great when you need a ground plane. We figured th=
at
> if we don't put anything on the bottom, we don't have to mess with alignm=
ent
> or double the exposure time.

We use double sided boards mostly, sometimes just for the ground plane=20
like you say (as you say no alignment issues) and sometimes for traces=20
too. For alignment we staple the masks together on two sides, around 2cm=20
from the edge of the PCB, as long as you get it near enough it works=20
pretty well.

> Vitaliy
>


--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.