sample qi story

7/31/2019 Sample QI Story

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THE 7 STEPS: A CASE STUDY

Step 1: Select Theme

Each improvement team at Analog has a written theme,with a specific, measurable goal, a metric, and a

timeframe by which it intends to reach its goal. In thistheme, the goal is to reduce occurrences of incorrectlyprocessed wafers in the photo area by a factor of 2, themetric is misprocessed wafers per million processed,and the time frame is nine months. (See Slide 6-2) Note

that the team avoided the use of the word errors, whichsuggests that human error is the cause of the problem.Instead, it used incorrectly processed wafers.

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Step 1: Select Theme (continuation)

Teams are often asked to try to verify why their theme isimportant, so that they understand it better and have a

feeling for its importance to the company. This teamshowed with a Pareto diagram that of all the areas in thewafer fab, the photo room had the highest incidence ofincorrectly processed wafers. (See Slide 6-3) Since this

affects yield and thus cost, the team demonstrated thatthe photo room was the right theme to work on.



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Step 2: Collect and Analyze Data

When the team first began to collect data, it found that theexisting forms used to report mistakes in wafer fab were

not useful. Moreover, operators were reluctant to provideinformation out of fear that the data could be used againstthem. The forms were traditionally completed by theirimmediate supervisor. As can be seen on this actual form

(recopied for clarity on Slide 6-4), the operator stated thatthe form is unfair and intimidating; the engineerssuggestion was to just follow the spec.



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Step 2: Collect and Analyze Data (continuation)

The team decided to collect its own data and make the formmore useful and friendly (Slide 6-5). In addition, it obtained a

commitment from management that errors would not be heldagainst operators unless the error rate was excessive.

When filling out the new form, an operator on the team satdown with the other operators involved in the incident,discussed the incident, and jointly wrote comments. The form

was then sent directly and in confidence to the productionmanager (that is, around the direct supervisor), so thatoperators would not have to fear recrimination for theircomments.



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Step 2: Collect and Analyze Data (continuation)

With data from their new forms successfully coming in,the team was able to focus on leading types of problems.One cut of the data (Slide 6-6) shows the team found thatwafers getting on the wrong track at the coat step andwafers receiving incorrect alignment at the align stepwere leading causes of incorrectly processed wafers in

the room. The team moved on to step 3.



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Step 3: Analyze CausesSlide 6-7 shows one of the early Ishikawa, or cause-and-effectdiagrams, the team created to determine the root cause of

incorrectly processed wafers at coat and align. Later diagramsfocused on the people, investigating why too many machineswere run at once, and environment, investigating why therewas a lack of space.

After further discussion and data discussion and data

collection, the team agreed on the root causes shown in Slide6-8, all dealing with either poor room setup and organization orpoor task assignment. The team verified these conclusions bysurveying all operators in the room.



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Step 4: Plan and Implement Solution

The team moved on to step 4, solution planning andimplementation, as shown in Slide 6-9. In their solution,the team borrowed concepts from just-in-time (JIT)methodologies, focusing on the use of kanbans toaddress the root causes found in step 3. The team alsoassigned responsibilities for each aspect of the

implementation, and a timeframe for completion (notshown).



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Step 5: Evaluate Effects

Slide 6-10 shows the teams evaluation of effects. The teamwas formed in March 1989, and implemented its solution

during August 1989. There were two special cases ofincorrectly processed wafers that were not related to theroot causes at hand, as shown by the peaks at July andDecember of 1989 and February 1990. However, the teamcontinued to implement and improve its solution, drivingdown the rate of incorrectly processed wafers until theproblem virtually disappeared by March 1990.

As shown in Slide-11, the room also reaped benefitsfrom JIT methods in the form of queue time reduction.



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Step 6: Standardize Solution

The team recognized that the use of the JIT principlescould decay over time unless the team performed step 6,

standardization. As shown in Slide 6-12, the teaminstituted JIT meetings every shift to discuss problems orimprovements for the system, with minutes of thesemeetings published daily. It also handed over the systemto the supervisors and operators in the room to run, and

agreed to meet only once per month as the Errorbustersto monitor progress and ensure that the gains were beingheld.



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Step 7: Reflect on Process (and Next Problem)

In step 7, reflection on the process and planning of futurework, the team agreed that the main thing it did incorrectly

was to focus on too many Pareto items during step 2, andthus on too many root causes in step 3 (Slide 6-13). Hadit focused more closely when taking data, it would havesolved the root causes one at a time and would havemoved faster because its attention would not have been

spread too thin. The team also decided to attack the nextlargest bar in the Pareto created during step 1, and thuswork on incorrectly processed wafers in the etch room.


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