LCD Project: SMT Tips from Julie S. Porter



SMT soldering is a lot like jewelry work. For hand work use separate flux.
Flatten the solder and cut it into little chips. Get a good bench magnifier.
Also get two sets of tweezers. One for heat, one never gets heat. A work
holder helps as well. A tiny bit of silicone seal can be used to hold the
chip in place, however the flux will often also do this. Remember solder is
not glue. It is a cement.  Flux is an anti oxidizer. Clean and flux the
joint well. Think hygienic. Place the chip of solder opposite the heat
source. This is where the tweezers come into play. I was always taught heat
the wire, not the solder. Solder will flow into the heat. As you noted the
capillary action will draw the solder. What was happening when you tried to
heat the connector. The holes got hotter faster. In Jewelry work it
sometimes helps to have a hot plate. It might also help to have a heat gun
to keep the work warm. Some multimeters have a thermocouple input. If you
are worried about burning the chip stick it onto the center of the package.
(Modern chips can take a lot of heat, too hot to touch.) I do not know if
this would work in or not. Jewelers also use silver solders and torches, the
process is the same. You might try clamping the parts with the holes between
sheets of metal to act as a heat sync. You can also cover parts you do not
want solder on with lacquer (fingernail polish.) Acetone will dissolve this.
Use Alcohol to clean the excess flux from the board. Use about 25% less
solder than you think you will need. It is easier to add solder than to
remove it.



As for the micro-machining it takes specialized equipment. Computer Numeric Control (CNC) machines, Electrical Discharge Machines (EDM), and precision lathes are not usually found in the home workshop There are suppliers such as J&L industrial supply (not on the web
1-800-521-9520) which has the small saws and end mills, even carbide circuit board
drills
Do not use a dremmel tool, the bearings are not precise enough. Used
watchmakers lathes can be had for in the 200 price range. Finding one of
these can be difficult, however they are traded on the net in the Horology
groups.

The following is pure speculation as to a way to homebrew a linear
positioner. It is based on a Kodak animation stand. Use a solid base, like
an oak butcher block, or an thick aluminum plate. I have even seen acrylic
used. 1/2 20 bolts can hold the work to this base. Get a good micrometer.

A simple slide poisitioner can be made from 3/8 40 TPI (thread per inch)
lamp rod and a nut.   This is what goes into the center of a lamp or
chandelier. There are some interesting fixtures used for mounting lamps to
wall and ceiling plates that have this thread. Places like Halted sell old
bearings. The rod acts as a lead screw. 360 degrees moves a nut ,or anything
attached,  1/40 of an inch. Be wary of backlash, only move the leadscrew one
direction. If you must reverse, always start from the same position, make
the mark/scribes then return the lead screw to the same spot by over
correcting the reverse direction, then moving it forward to the mark. (a
micrometer works the same way.) The whole thing is mounted in Pillow blocks,
which are stocked in most respectable hardware stores.

The screw can be used to move a drafting or resist pen. It might also move a
scriber, which will cut through the copper. It might even hold a soldering
iron (then you would have a rework station). Again a dremmel is not precise
enough. A dial in placed on one end of the screw indicating how far to turn
to move a specific distance. A bit of trigonometry is required here. A
second positioner mounted 90 degrees to the first can be used to move the
pen back and forth. If you add steppers you have an XY plotter. In this case
you can move the work and keep the pen steady. There will have to be
provision to move the pen or work up and down.
A set-screw in a sleeve can be used to lock the lead screw.
The board is etched the usual manner.

More speculation for cutting traces for SMT layouts. This from a biscotti
maker.
I'd etch the board first and leave the connector a solid block, then cut the
traces apart.
J&L sells slitting saws. Get the type that are 1 inch in diameter They
should be the thickness of the non copper space. Mount an arbor between
pillow blocks. The saws are mounted onto this arbor with spacers the exact
distance of the trace apart. To make the spacers get a soft washer (brass or
copper), A sheet of glass, sand paper and a cork. Glue the sandpaper to the
glass. hold the washer with the cork and sand it until it is the distance
needed for the pitch. Use a micrometer to measure the spacer.
I'd recommend turning the saws by hand and scraping through the copper.
Rotating them with power requires a guard, carbide is brittle and can break
apart. (See the ring cutting scene in the Beatles movie HELP!)

Most of the board (and even chips) are made with photolithoghrapy
(Printing). Even some modern watch parts in mechanical watches are etched.
Film has a resolution around 8000 lines per inch or 16000 dpi. (some give it
as 4000lpi and 8000 dpi. Lasers can take things down to the wavelengths of
light. On a more practical nature, there are LaserToner transfer systems. I
have had mixed luck with these. What happens is laser ink is plastic and
melts at low temperature. The transfer is a sheet of water soluble glue.
This is an electrostatic process. The layout is printed on this paper. Then
it is heat transferred to the copper. I have found that it take a lot of
work with a resist pen to get a good board.

Standard board manufacture is done with film. This is great for production
runs, but difficult with home brew. It might be possible to do a simple
multi layered boars with the fiberglass products sold by boatmakers. I was
told vias are done two ways. Plate through where the copper is plated onto
the fiberglass after the holes are drilled. The other is rivet. Where copper
plugs are driven into the board then, riveted over. This has two drilling
steps, but almost sounds like it could be done on a small scale basis. It
might be possible to homebrew a 3 or 4 layer board (would be pretty thick)
using the boatbuilders stuff sold at TAP plastics (do they have TAP outside
the Silicon Valley?) This stuff uses UV to harden. It comes in two parts, a
fabric, The fiberglass, and a resin. (the resin is also in parts.) I would
start with a sheet of copper clad. Etch Both sides. I would rivet in the
vias having them stick through the fabric. The top board would be pre-etched
and drilled to match. The whole thing would have to be mounted in a press
and cured. The vias would then need to be riveted over on the outside and
drilled out.

There is also copper tape, used by stained glass artists. Halted stocks this
as RF shielding. It has a sticky side and a foil side. I got some, and am
planning on experimenting with it and some plastic sheet, to make some
flexible connector boards.

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julieP