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Solder Alloy Leads to Broken Glass



Solder Alloy Leads to Broken Glass
A manufacturer of defroster windows was breaking thousands of dollars of windows due to a soldering problem. What was causing a change in the solder alloy?
Mysteries of Science

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Transcript


Have you ever wonder how defroster windows work? Electrical current is applied to a heater pattern built right into the window. The electrical current heats up the strips that are typically configured as a set of thin dark lines made with metallic ceramic ink that has just the right resistance to heat up.

But how do you attach wires from the window to the vehicle's electrical system? The ink is made with enough metal powder to allow wire or metal connectors to be soldered to them.

One day the solder supplier got a call that something was wrong and they were breaking thousands of dollars' worth of windows every day. What could be going wrong?

Solder was applied to the connector tabs by dipping them into a molten solder bath and there wasn't much that could go wrong with that process.

Was there a change in the solder alloy? If the alloy changed, the assemblers might turn up the soldering iron settings or press harder when the solder doesn't melt within a few seconds.

But the soldering tools were not running hot and the solder alloy was right on target, so solder was not the culprit. But the auto manufacturer was sure that the solder was involved in some indirect way and here's why.

Every time the solder vendor went out to visit the plant, the yield went up dramatically and hardly any windows broke. But while the vendor was away, broken windows set new records.

Most everyone decided that it still had something to do with overheating of the glass, and maybe the workers were just extra careful when being watched.

So they tested a technique using conductive adhesive. The following week, samples were brought in and tests were started. The adhesive was more expensive than solder since it contained mostly silver power while the solder was made from tin and lead.

The vendor argued that the new process would cut labor costs and the higher materials cost was inconsequential. The vendor continued to make a case for this labor-saving breakthrough and pointed out that broker windows would drop to zero.

One of the workers, who was on break, was fascinated by the new technology since it looked like solder that soldered itself. So he asked questions until he had a good idea how it all worked.

He also recognized that he could be replaced since this process, if it worked, would need less than half as much labor as the old soldering iron method.

The following week, the yields went to 100% for the old soldering process. This wasn't a fluke because the same thing happened during the following week, and again on the 3rd week. So what's was going on?

Here's the rest of the story.

One engineer solved the mystery. The workers had a grievance that wasn't being handled too their liking, but it wasn't worth a strike. So they were cranking up the soldering irons and breaking windows. It may sound dumb, but this happened in the days when companies and workers acted like they hated each other.

But what fixed the problem? Once the line workers realized that conductive adhesive would fix the problem and probably get rid of a few workers, they decided to bring stop to their destructive tactics.

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