How clean should an assembly be? The answer is clean enough. What
climatic conditions? What type of residual ions? What reliability? What
lifetime? What components? What make of instrument? What testing
solution? What temperature? Etc. Even if I had the answers to all these
and other questions, I still couldn't give you a figure in µg/cm² eq.
NaCl. The only way of handling this type of question is to make up a
batch of 20 or 30 assemblies and clean them as you do habitually,
knowing that they are unlikely to cause problems in service. Measure the
ionic contamination on each one and determine the arithmetic mean and
standard deviation (SD) of the batch. Draw a histogram of your results
and superimpose the SD curve. Are they of similar shape without undue
skew? If so, your process is reasonably well controlled. I would suggest
you do subsequent tests, say, 5 x /day, assuming continuous production.
If the results fit consistently within the SD curve for a given number
of tests, or thereabouts, you know your process is under control and you
can sleep tranquilly at night with both ears on the pillow. If you see
the results starting to drift away from the SD curve, either you are
wasting money by over-cleaning or your cleanliness is becoming doubtful.
For further info, see pp 250-257 of a well known book that explains this
statistical approach, which I have advocated since 1979, when I put the
first computerised ionic contamination tester on the market, with
software that used this method automatically. It gives typical
acceptable and unacceptable SD curves. In my opinion, this is the only
logical way of using such instruments.
Brian
On 24/01/2011 13:43, Forrester, Michael (H USA) wrote:
> I have a basic question. What is the industry standard on checking
> PCA cleanliness?
> Basically there are various methods (ROSE, IC, etc..). For a standard
> SMT
> production line, is the testing done once a day, week, batch, etc.. I
> understand that the
> testing is to be used as a process control. Maybe some SMT lines get
> the process
> under control and don't do testing? What should the total ion
> contamination on a standard
> SMT PCA be below for a standard SMT PCA? Thank you.
>
> Best Regards,
>
> Michael Forrester
> Sr. Product Engineer
>
> ______________________________________________________________________
> This email has been scanned by the MessageLabs Email Security System.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/ContentPage.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
> -----------------------------------------------------
>
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/ContentPage.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
