Decisions and Analysis

CASE STUDY: REJECTED CIRCUITS

An electronics manufacturing company is involved in the demanding task of producing miniaturized printed circuitry. One day, the production quality fell off sharply and the number of rejected circuits skyrocketed. “Why?” demanded the manager.

“Temperature in the leaching bath is too high,” said one technician. So the temperatures were lowered.

A week later, when rejects climbed still higher, temperatures were raised, then lowered again, then systematically varied up and down for days. Rejects remained astronomical. “Cleanliness is not what it should be. That’s what’s causing the trouble,” someone offered. Everything then was scrubbed, polished, filtered and wiped. The rejects dropped, then rose again. Acid concentration was the next idea. Same results followed. Water purity was checked out on Wednesday, Thursday and Friday. The possibility of oil transferred from the operator’s fingertips received full scrutiny on the following Monday and Tuesday. Rejections were still high.

They might have remained high had one supervisor not begun to ask systematic questions. “What is wrong with the rejects?” This returned the information that the acid leaching step of the printed circuit pattern was occurring unevenly – as if some waterborne contaminant in the leaching solution was inhibiting the action.

“When does it occur?” A check of the records showed that rejects were at their highest on Monday mornings, lower on Monday afternoons and gone by Tuesday noon.

This cast a different light on everything. Now, nobody was asking ‘why’ about the cause of a general, ill-defined deviation. Instead, they focused on ‘What was distinctive about Monday mornings’ compared to the rest of the week. They focused on what might have been changed that bore a relationship to this timing. An immediate distinction was recognized. “Monday morning is the first work period following the non-work period of the weekend.” And what changed on Monday morning?...