We're in a modern factory with a recently completed building that is making printed circuits by a revolutionary process called Polymer Thick Film. The concept is to print conductors, resistors, insulators, and eventually components, directly onto material. This material can even be a roll of plastic film.
the idea has been around for many years, this was the first significant
investment in the technology and this company was betting everything on
this unproven way of making circuits. Most circuits are made by etching
away copper foil that has been bonded to a dielectric material, a more costly
and much more wasteful process than Polymer Thick Film.
factory had new equipment and was evaluating inks. After 3
months most of the processes where under control and the first high-volume
product was ready for launch.
The circuit conductors were made by printing
metallic ink and then dried in a long oven. Then carbon resistor ink was
printed so that it contacted the hardened metallic conductive ink.
drying, the resistance values were measured and the printing
process adjusted until the values of the printed resistors were within
The process was under control, and the customer was pleased
with the product. More orders were placed.
carbon ink supplier was a small firm in Minnesota and the circuit company was
worried about reliance on only one supplier. The suppliers ink
was always perfect, but one day it was too thin making it print poorly.
There was panic since production only had a 3 day supply. Calls to the ink
supplier did not indicate anything had changed, and the ink analysis in
the lab did not reveal any issues.
R&D manager decided to review every step. There was nothing they could
pinpoint. Even the plant temperature and humidity were checked. The manager
also reviewed packaging and shipping. The packaging was simple; a wrap in
a poly bag, seal it, put it in a box, and delivered to UPS.
So what was going on?
the rest of the story.
R&D manager wanted a shipping timeline comparison. The finished ink was
poured into plastic containers and then placed in the shipping area so their
truck could load it in the morning and drive it to UPS.
"How cold does the
shipping area get overnight", the R&D man wanted to know. "It gets
quite cold here since the place isn't insulated, but that doesn't matter
anymore since we started storing the ink inside", said the ink maker.
"When did you start storing the ink inside?" asked the manager.
"We just started doing that on the last shipment", was the reply. Was
this a clue?
me a favor", requested the manager, "put some ink in the loading area
tonight and ship it tomorrow, just like you did last week". The ink
arrived, and sure enough, it worked fine.
on this insight, the lab manager placed a container of "thin"
ink in the freezer. The next day, the ink was allowed to warm up, and then it
was tested. The ink performed perfectly.
The freeze cycle was the key.
Apparently, the low temperature caused the plastic binder to thicken. This is
just the opposite of many inks that thicken if warmed up for a while, so it was
hard to spot.
solution was to "age" the ink by chilling it. It turned out that
the ink thickened naturally after a week or two and then became quite
stable. The rapid production ramp-up didn't leave enough time for natural
aging so the "chill aging" was needed.
The lesson here is to analyze
the entire process and never assume that any step is unimportant.