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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 23 Feb 2000 09:08:50 +0100
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Bernhard

I could not disagree with you more. Many components I have tested with
an ionic contamination tester have revealed levels of 12 - 24 ug/cm2 eq.
NaCl (compared with c. 1,5 ug/cm2 eq. NaCl as typical old spec levels).
Many component manufacturers use hydrochloride-activated W/S fluxes for
hot tinning with just a perfunctory single spray of water, rarely
changing the water. These residues may be totally insoluble in solvents
and, in time, even in water. They may, however, alter the reactivity of
the subsequent soldering flux and, in the case of "no-clean", give a
very reactive residue, leading to untold problems. I pointed this
problem out in three of my books published in the 1980s and this is the
reason my company, at that time, developed a tester for components.

IMHO, there is no such thing as "normal" contamination. The only things
that should remain on a "no-clean" assembly are the flux residues and
by-products. "No-clean" is a misnomer, especially if you wish
reliability: it means that you displace the cleaning processes to the
bare boards and other components before assembly and you make sure your
assembly process does not introduce any other contamination. Only that
way can you be sure that the flux residues are benign enough to perform
as the manufacturer intended.

This is the main reason why SIR testing is, in many cases, useless to
qualify a flux: you qualify it under lab conditions, totally ignoring
the fact that its behavious will alter in practice due to it mixing with
external contaminants not present on your test vehicles.

I cannot emphasise these points too strongly: I have seen much damage
caused by contaminated components, even to the point that the component
leads themselves have been corroded through. And don't think that this
is confined to hot-tinned ones - I have seen electroplated leads equally
bad.

Now, there's something for Doug, Graham and others to chew the rag over!

Brian

> Wanner Bernhard wrote:
>
> Probably its not a real problem, because...
>
>    * if you are cleaning your pwa's anyway, you will clean also the
>      components,
>    * if you use clean-free, you will take accept also all your
>      "normal" internal contaminants (flux, fingerprints ..) and most
>      component-contaminants will be at a similar level/kind.
>
> I like it, Dougs :"...YOU determine ..". hehe, that's exactely what
> you have to do, but instead of to write own standards I would refer to
> the golden IPC-octuple (you don't know it? so what!: IPC-2221, -2222,
> -6011, -6012, -4101, -A-600, -A-610, J-STD-001, all class 2, and
> IPC-D-279 + IPC-HBK-001 as guidelines).
>
> Bernhard
>
>      -----Ursprüngliche Nachricht-----
>      Von:    Douglas Pauls [SMTP:[log in to unmask]]
>      Gesendet am:    Dienstag, 22. Februar 2000 19:42
>      An:     [log in to unmask]
>      Betreff:        Re: [TN] components cleanliness
>
>      In a message dated 02/22/2000 11:50:09 AM US Eastern Standard
>      Time,
>      [log in to unmask] writes:
>
>      > Is IPC has requirement for component cleanliness?  I have
>      checked archives
>      >  of TechNet.  No IPC requirement in Sept. 1998.  Anything
>      changed?  As Bev
>      >  Christian stated 2 years ago:
>      >   "No company can really afford to carry a complete set of its
>      own standards
>      >  any more and with the contract manufacturing industry out
>      there, it doesn't
>      >  even make sense to try and do it."
>      >   Help!  (with components comming from anywhere and everywhere,
>      standards
>      are
>      >  needed)
>
>      Joyce,
>      Don't hold your breath.  With the move towards performance based
>      specifications, most IPC assembly level specifications are going
>      the route of
>      having the assembler or OEM define for their hardware what
>      cleanliness
>      measures are to be used and what cleanliness requirements are for
>      their
>      products.  From a cleanliness standpoint, I don't foresee any
>      more "one size
>      fits all" cleanliness specs.  Them days is gone.  I think about
>      the best you
>      will see will be recommended protocols from the IPC on how YOU
>      determine
>      cleanliness of components and how YOU determine how clean your
>      components
>      need to be for your hardware.
>
>      Doug Pauls
>      Technical Director
>      Contamination Studies Labs
>
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--
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

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