On Fri, 20 Feb 2009 20:27:33 -0000, you wrote:
>Hello,
>
> Since encountering this group a month or so ago, I have refined my
>toner transfer process to the point that I am able to reliably do 15-
>mil traces. Maybe smaller. Hope so.
I'm roughly at 10 mils, 12 is run of the mil.....
>
> I'm doing a home project and have settled on PIC24F
>microcontrollers. The latest version needs USB, and all the PICs
>that support USB are surface mount. So I have been dragged kicking
>and screaming into the 21st century.
Ain't Technology wonderful?
>
> I bought an Aoyue 968 hot-air SMD rework station and some fine
>tweezers and have been having a good time scrounging parts off some
>defunct computer boards - just to get used to the tool. I'm going to
>need a microscope - half of these parts just look like bits of dirt!
Yeah, now try to measure them. Seems to be the 50 dollar solution and
the 350 dollar solution, other than the 10 dollar ebay tweezers
(only).
I prefer 1206 or 805 at the smallest, just because of ease of using.
You're probably getting 4xx or so.
>
> One part I scrounged is the same package as the 24FJ256GB106
>processor I'm planning to use - a 64-pin TQFP. Good LORD those pins
>are small. Can Toner Transfer make boards this tight? According to
>the spec sheet, the pin pitch is .5mm, or about 20 thousandths of an
>inch. So the traces need to be 10 thousandths of an inch, and will
>only have 10 thousandths of separation. Ouch.
In theory, yes. You might find yourself using 8 mm traces, or 10 mm
traces and somewhat larger pins. I inadvertently made a board with
0.5 mm spacing pins on one 4 pin connector, and it turned out semi
"OK". The whole board was a bit over etched, so the pins did not look
as nice as I would want, but otherwise ok, I'd suppose.
You'll either want a small tip (almost a needle) soldering pencil for
the leads, or you'll want to tin-lead coat the pads before soldering.
Very find gauge solder is also a must. I find that upon occasion, a
larger soldering iron to solder multiple pins at once, and a
desoldering tool (built in air pump kind, not spring release) cleans
up things nicely. NOT elegant, I know.
If you had the right stuff, then a syringe of solder paste and your
hot air pencil would be the optimum method. (Right stuff defined as
right tools and paste, etc...)
Yeah, possible to do, messy, and then there's the matter of vias...
An alternate option is to use a carrier, such as the schmartboard
carriers, and go from there. Chip will be on a carrier that's 2
inches by 2 inches. Decent for prototypes...
Harvey
>
> - Jerry Kaidor
>
>