TECHNET Archives

March 2000

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Gary Camac <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 27 Mar 2000 15:48:54 -0600
Content-Type:
multipart/mixed
Parts/Attachments:
text/plain (5 kB) , gcamac.vcf (5 kB)
Good afternoon everyone,

A few years back I used  Ionograph testing to try and prove statistical control of my in-line washing process.  I was always within the spec limit, but I could never show a normal distribution.  The data was collected from tests on all varieties of assemblies: single and double sided through hole, and single and double sided mixed technology.

Then it dawned on me that I was throwing apples and oranges in the same crate.  Since the topography of these assemblies are different,  I concluded that I needed charts for each assembly type.  Hmm....quess again Sherlock.  Once again I could not get a normal distribution.

I could  not come up with any assignable causes to explain the lack of a normal distribution.  Since I never had any test outside the spec limit, I had a hard time justifying putting more of my time in the effort.  As you all know, you have to know when to fish and when to cut bait.

Lou Hart wrote:

> TechNetters,  (and Brian), I suggest looking into statistical process control techniques for something like this.  A standard Shewart chart would be the thing.  In fact, I plan on doing it myself in the very near future, thanks to Brian's earlier suggestions on cleanliness testing techniques.
>
> If you take 1 standard deviation as a "control limit" you'll have lots of false alarms.  The purpose of SPC is not so much to tell you when to do something, but rather when not to do something, to leave things alone.  A while back, a technetter said he'd made a chart, but found points always inside the limits.  That's exactly the way things you want things to be.  Go to work on something else and don't waste time tinkering with a well-behaved process.  Unless it is producing bad stuff, in which case you need a new process.
> Lou Hart
>
> ----------
> From:   Brian Ellis[SMTP:[log in to unmask]]
> Sent:   Saturday, March 25, 2000 8:12 AM
> To:     [log in to unmask]
> Subject:        Re: [TN] process control of final cleanliness in a no-clean world
>
> Wade
>
> I agree with the others but would add one minor point. Qualify your
> process as "safe" according to your needs. Measure the ionic
> contamination with whatever instrument you will on, say, 20 boards from
> a similar batch, keeping the test going to near-asymptote (say less that
> 1% conductivity change in one minute). Note these final values and
> calculate the mean and standard deviation (ideally, the distribution
> should be a neat bell-curve). For that type of board, run regular tests
> in production: if they fall significantly outside the mean +/- SD
> (either higher or lower), then your process is probably going off the
> rails. Note that a lower reading of contamination may be just as
> dangerous as a higher one, because it signifies a change in the process
> parameters.
>
> Brian
>
> "Oberle, Wade" wrote:
> >
> > Dear technetters,
> >         How do all of you in the no-clean world monitor and control board
> > cleanliness.  In the days of OA flux, we used an Ionograph or Omegameter to
> > monitor our 'cleaning' process.  Do some of you still use an ionic
> > contamination tester or do you use SIR testing or nothing or what?
> >
> > Thanks in advance for your advice.
> >
> > Wade Oberle
> >
> > ##############################################################
> > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> > ##############################################################
> > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> > the body:
> > To subscribe:   SUBSCRIBE TECHNET <your full name>
> > To unsubscribe:   SIGNOFF TECHNET
> > ##############################################################
> > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> > information.
> > If you need assistance - contact Keach Sasamori at [log in to unmask] or
> > 847-509-9700 ext.5315
> > ##############################################################
>
> --
> Brian Ellis
> Protonique SA
> PO Box 78
> CH-1032 Romanel-sur-Lausanne, Switzerland
> Voice: +41 21-648 23 34 Fax: +41 21-648 24 11
> E-mail: [log in to unmask]
> URL: Technical and consultancy divisions:
>        http://www.protonique.com
>      Web services division:
>        http://www.protonique.com/webserv
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> the body:
> To subscribe:   SUBSCRIBE TECHNET <your full name>
> To unsubscribe:   SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> the body:
> To subscribe:   SUBSCRIBE TECHNET <your full name>
> To unsubscribe:   SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################


ATOM RSS1 RSS2