TECHNET Archives

May 2001

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:
"Creswick, Steven" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 17 May 2001 07:42:58 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (135 lines)
To add some spice to the soup, I would like to comment on the wetting
characteristics of a WS vs NC flux on Pd/Ag thick film metallization.

As a IMHO comment, the WS does NOT wet as well as the NC in THIS
application.  The WS flux does an excellent job of wetting WHERE IT HAD BEEN
DEPOSITED, however, we saw very little spontaneous wetting across pads not
covered by the initial solder paste deposit.  Whereas, a NC flux will tend
to flow beyond the point of initial deposit and allow extended wetting.
Standard RMA's being the ultimate in extended pad wetting.

We attributed these characteristics to the WS flux burning off early,
leaving nearby (non-solder-covered solderable) areas unaffected, whereas the
NC fluxes tended to 'passivate/activate' the surrounding non-solder-covered
solderable pads during reflow.  The RMA's were the ultimate in
passivation/activation.


Having said all that, unless the PWB is badly oxidized, I do not see how the
WS flux can NOT wet better than the NC due to it activity level!

..... IMHO

Steven Creswick
Gentex Corporation


-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Thursday, May 17, 2001 4:22 AM
To: [log in to unmask]
Subject: Re: [TN] No-clean vs Water-soluble wetting?


Rick

The activity of typical water-soluble fluxes is approximately 1,000 to
10,000 times higher than that of typical "no-clean" fluxes. Of course,
like all generalisations, you will find exceptions to this statement.
After soldering, the ratio of the activity of the residues will have
dropped by an order of magnitude, because the hydrohalide activators in
the W/S will have largely decomposed at soldering temperature, while the
comparatively poor sublimability (if there is such a word!) of the
dibasic carboxylic acid activators in the N/C (usually) will mean that a
large proportion will remain.

The high activity of W/S means that it can be used for solder wetting
almost any reasonable and solderable surface, even if fairly heavily
oxidised. The low activity of the N/C means that it will allow
solder-wetting of only clean, very solderable, surfaces which are not
heavily oxidised. In other words, not only does W/S promote fast, wide
and reliable wetting, it offers a much wider process window which
pardons many errors, whereas N/C offers a very narrow process window
with little margin for error. Anyone who has worked with both will know
that the retouch rate (expensive) with N/C is often as much as an order
of magnitude higher than with W/S, all other things being equal and
optimised.

Of course, the down side of W/S is that you MUST clean and you must
clean demonstrably well (although it is not difficult). I also say that
the down side of N/C is that you should not clean, under most
circumstances, because the flux is not formulated to be cleaned and
cleaning may actually reduce the reliability under some of these
circumstances.

I suggest you may care to buy wour QA manager any of the usual books on
soldering, such as Klein Wassink, Manko, Strauss etc. or that he simply
speaks to your paste vendor's technical guys.

You think right.

Brian

Rick Thompson wrote:
>
> I've been having an ongoing discussion with our QA Manager regarding the
> wetting capabilities of No-clean versus Water-soluble solder pastes.  He
> believes that no-clean wets better, I think the opposite. This is in an
air
> reflow environment. I'm curious as to what some of you might have to offer
> on the subject?
>
> Thanks in advance,
>
> Rick Thompson
> Ventura Electronics Assembly
> 2655 Park Center Dr.
> Simi Valley, CA 93065
>
> +1 (805) 584-9858   x-304  voice
> +1 (805) 584-1529 fax
> [log in to unmask]
>
>
----------------------------------------------------------------------------
-----
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> 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 delivery of Technet send the following message: SET
Technet NOMAIL
> Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
> information, or 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 1.8d
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 delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or 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 1.8d
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 delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------

ATOM RSS1 RSS2