Abdullah,

Assuming that by defect you mean a product characteristic not
meeting spec, that by process indicator you mean a product
characteristic meeting spec but showing some undesirable feature
that would lead you to adjust the process, and that both are
attributes, I would do the following:

For process control:-

Chart both defects and process indicators on the same attribute
chart. Special causes can cause a change in the incidence of
process indicators as well as defects.

For process capability:-

For attributes, process capability is represented by the average
level of defects after the process has been brought into control. I
would just use defects here. Including process indicators would
effectively be changing (tightening) the spec.

Have you done a process analysis to identify critical process
parameters? You will benefit if you control them.

Try and get hold of:

IPC-PC-90 General Requirements for Implementation of Statistical
Process Control

and

Understanding Statistical Process Control
Wheeler, Donald J and Chambers, David S
SPC Press Inc
ISBN 0-201-54405-9

Just my tuppence worth.

Rick Price
[log in to unmask]

On 15 Jul 98 at 16:19, KRIMLYA AT AEC wrote:

>Date:          Wed, 15 Jul 1998 16:19:23 +0300
>From:          KRIMLYA AT AEC <[log in to unmask]>
>Subject:       SPC

>Dear Tech Net:
>
>We are an electronics company located in the middle east and a member of
>IPC, we are implementing SPC and are having problems with Process
>Indicators, our questions are:
>
>   1- Should process indicators be placed into the same control chart as
>defects or should they be placed into a separate control chart.
>   2- Should process indicators be included in capability studies, should
>they be in the same capability study as the defects or should there be a
>separate capability study for process indicators.
>
>
>Best Regards
>
>Abdullah Al Krimly
>Industrial Engineer
>AEC SPC coordinator
>Advanced Electronic co. Ltd.
>P.O Box 11623
>K.S.A.
>e_mail: [log in to unmask]
>
>

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