Homebrew_PCBs

Gentlemen,
Stefan asked for more information about my Roll Tinning Machine. I expect
others may be interested.

I have loaded several pictures into the photo section.

To gauge the size of the machine the main roller is 300 mm x 100 mm cored
steel. ( Steel pipe with a 10 mm wall thickness)

This roller sits in a bath of molten 60/40 solder. The bath is about 50 mm
deep. A temperature probe is fixed in the bath just below the roller.

A 2000W element is mounted under the solder bath in contact with it. The
bath is made of 6 mm steel.

There is a 12 mm piece of insulating board beneath the element.

The top roller is made of silicone rubber on a steel shaft.

To use the tinner the bath is heated up to 244 degrees C and the motor
drive turned on. A fairly corrosive flux (radiator soldering flux) is
floated on top of the solder on the back side of the roller. Once the
roller has been rotating for several minutes the solder will flow evenly
over the roller.

When this happens the rubber roller is screwed down to the surface of the
solder roller.

The printed circuit boards are cleaned with a tarnish remover and dipped in
a water soluble flux.

The board is then fed through the roller from the front.

If the board is double sided it is dipped in the flux again and put through
the rollers again upside down.

This process gives a very clean solder layer over all the tracks.

David

--- In Homebrew_PCBs@yahoogroups.com, David Hopkins <davhop@b...>
wrote:

> Gentlemen,
> Stefan asked for more information about my Roll Tinning Machine. I

expect

It was hand made.
However a machine shop was available.

David

At 06:18 PM 18/01/2004, you wrote:

On Mon, 19 Jan 2004 05:32:12 +1000, David Hopkins <davhop@...>
wrote:

St,
The roller was made by a company that specialize in this You give them the
steel rod and tell them what diameter you want.

I don't know if it is the same as the rubber used in printer rollers. This
mob make a mould and mix the components and pour it into the mould.

They put the roller into a lathe and turn the oversize rubber down to size.

So long as the rubber can withstand the temperature it should be ok.

The steel roller is machined to have a smooth surface.

The machine is about ten years old. Recently the roller started to pit and
I had to refurbish it.

I removed the roller and placed it in the lathe. I turned about a
millimeter off the surface until it was back to bear metal. The roller was
put back in the machine and the solder heated. Flux was floated on the
surface and the roller rotated for about ten minutes. By this time the
solder had evenly coated the roller and we were back in business.

The main drawback of the whole process is the flux used to allow the solder
to coat the roller. It is very corrosive but essential.

When the machine was first built the people who built it could not get it
to work and gave it to me. They were using 100% tin instead of solder and
could not find a suitable flux.

I got it going by replacing the tin with normal solder and the current flux.

Over the years we have tinned hundreds of boards with few problems.

As I said above corrosion is the main problem. I have replaced the bearings
twice, the solder tank once and skimmed the roller.

David


At 12:35 AM 20/01/2004, you wrote: