making small boards

[fowardbias]

I haven't made a CB in many years ( jr. college). It was a process of using a photo neg. as a mask to develope the sensitive board material. Lots of chemicals and timing was a big part of it also. The boards had the old huge large traces for DIPS and larger components. Question:
What is the better way to make a modern small board with mostly SOIC and surface mount R's and C's. The boardwill be .75" x 1.25" single sided. The plan is to hand make 5 boards. field test and improve ,then make a run of 50 or more. I am using Eagle Draw and I believe the files generated in the router will be accepted by the different small run board houses if I go that way. I am not sure if detailed small hand made boards are even possible. I have hand soldered 805 and 603 size components but am unsure as to the quality of the etch. IDEAS?

[mackrackit]

I use positive presensitized boards for my prototyping. No problems with SOICs.

Print the art work on a transparency.
Clap the transparency to the board with a piece of glass.

(Now for the strange part, I do not have a light box. I live in SW Arizona.)
Set the board, artwork, glass clamp up out side for about 20 minutes. Double sided, flip in 15. You can see when it is finished.

Chemicals. I then use a weak solution of KOH to remove the reacted coating. Rinse with water and etch with ferric chloride.

Not a big deal.

Not sure about Eagle, if it will make a gerber file it should be fine.

That is my two cents. :)

[duncan303]

but am unsure as to the quality of the etch

Qualities of etch on “home made” boards IMHO tends to be largely dependent on

A: the negative being able to act as an effective UV block (proportional to ability of printer to deliver an adequate density of ink/toner) and (crispness of edge, dependant of printers method of placing ink/toner), the proximity of the negative to the pre-sensitised board (think penumbra)

B: cleanliness.

C: The rate of reaction of the ferric solution at the copper interface coupled with phase distribution. Think fast etch with a uniform solution, normally achieved with a heated solution in a bubble/agitation/spray tank with the boards held vertically.

D: and cleanliness.

I have used the Sun before :) its good fun, somehow ads a positive eco tinge to an otherwise totally un-eco, planet destroying, poisonous hobby.

Advantage: UV source very narrow (penumbra). Free for the moment

Disadvantage: UV intensity relatively low (where I am certainly) and degradation to the negative through heat absorption (unwanted wavelengths) and material transfer, ie negative can adhere to the resist. I always use a “very” light dusting of talcum powder anyway even when in the UV box.

So therefore I will add speed of exposure as another factor in the success with home made boards.



I am not sure if detailed small hand made boards are even possible

Of course this probably depends on how adept a person is in a practical sense, coupled with some basic science/engineering knowledge together with a light sprinkle of physical chemistry. Most certainly the desire to experiment and be able to “see” and resolve any problems rather than viewing through a casual observers “eye” is essential. If the limit of a persons “hands on” experience ends at pressing keys on a keyboard then I would advise them to have a board house produce their PCB. I use Eagle and using the CAM processor all board houses are available, the choice is the specification limits of the boardhouse not the ability of any dedicated CAD software. There is generally not a PCB minimum size specified by boardhouses (excluding border), so rather than keep the scale of any design large enough to work on “old style” go miniaturisation. Everything is cheaper; components; PCB; materials; everything. It can assist in reduced RF/EMI I can think of no disadvantages. So therefore the cost of having even a single prototype produced by a boardhouse becomes negligible compared to “home made” consumables cost. And the cat doesn’t have to lose it’s litter tray for half an hour :D

One of the main arguments, other than prototype speed vs cost, given by salespersons of professional CNC machines is that although the PCB’s produced are unable to match the specification of boardhouses, they allow commercial privacy to pre-release products and keep development “in house” without specialist skills. Of course there is merit in this argument if those are of genuine concern. However I would still invest in the most powerful illuminated desk magnifier and soldering station one can afford and get practising.

Eeerrrr Rambling on again.

I really do need to get a hobby!

Duncan

P.S I do not have a cat, and I am unable to offer any rational explanation as to why I seem to keep inventing ownership of one.

[mackrackit]

P.S I do not have a cat, and I am unable to offer any rational explanation as to why I seem to keep inventing ownership of one.
It is your subconscious telling you to get one.
If you can teach them to keep off the key board and teach them not to play with wires let me know. :)

[Ingvar]

Keyboards ... forget it, cats just LOVE keyboards.

Wires ... no need to teach them, they learn on their own. I had a cat that loved to chew on cables. One day he acted really strange and never chewed on a cable again. Later i found bitemarks in my computers powercord ......... needless to say that it's always plugged in.