Scott,

Wave solder is always the process people turn to in when they want to
'implement SPC'.  I would always answer your question with a question -
"What do you want to control?".

As you know there are many parameters which can affect the quality leaving a
wave soldering machine but most of them should be controlled by the machine
e.g. temperature, speed etc and provided the machine is checked for
calibration these would not benefit from the use of SPC.

Once a process is set up correctly, the biggest influence on the quality of
the output are the parameters which are difficult to measure (at least using
SPC on line) e.g. board design, solderability etc.  for this reason I would
advise the use of attribute charts to measure the quality of the output.  I
know many quality people think this is not "proper SPC" but it is and can be
used to make improvements.  I would use 'p' charts to measure defects per
opportunities or np charts if you are prepared to have a separate chart for
each board.

This type of chart also fits in well with the draft document IPC 9261 and
maybe one day we'll be able to benchmark each other against this standard
(if anyone will release their data!!)

This type of chart will then give you a handle on how well the process is
operating over time and what type of variability you see.  The hard bit is
then improving it!  The chart obviously doesn't do this for you but it does
help you decide whether you have REALLY improved the process.  In making
improvements I often find it useful to have a number of copies of the board
layout and mark them up as measles charts using different colours for
different faults.  This simple technique is really useful at identifying
trends due to design etc.  And the more information you record the more
useful they become e.g. pallet number, date, time, shift etc.

My final question would be why are you implementing SPC.  If it is to meet a
quality requirement to use 'statistical methods' then I would suggest that
you meet this by using a broad range of statistical tools to improve your
process and not just go down the old 'we must implement SPC' route.  For
example if you want to trial a different process, flux etc.  use statistical
methods (e.g. Chi Squared tests using contingency tables) to compare results
and prove any change / improvement.

I would always advocate the use of statistics to prove a hypothesis but only
use SPC when you need it, don't go looking for a use for it.  If you are
already measuring data on a standard chart etc it may be worth looking to
change that to an SPC chart and start working with limits etc.

Good luck,

Neil

-----Original Message-----
From: Rougeux, Scott [mailto:[log in to unmask]]
Sent: 04 October 2001 15:02
Subject: SPC @ WAVE SOLDER


In regards to SPC at wavesolder. I would just like to here from some of the
people in this forum on what type of data they are collecting or sampling.
Any info is beneficial. Thanks.

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