Hi Keith,
Could you please provide more details of the "stabilised variant of the
Sn-07%Cu eutectic" that your company has developed? I have not heard of
this before, only of the "standard" Sn/Cu eutectic which has been around for
years.
Regards,
David Suraski
----- Original Message -----
From: "Keith Sweatman" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 23, 2001 9:25 AM
Subject: Re: [LF] Lead Free Board Finishes
> Hi Thomas,
>
> Over the past year or two something approaching 20 million boards, ranging
> from single-sided to multilayer have been wave soldered under commercial
> production conditions (for commercial use) with the stabilised variant of
the
> Sn-07%Cu eutectic that the company with which I am associated has
developed.
> In many cases wave soldering is carried out after one or more reflow
stages.
> For reasons of economy most of these boards have a resin preflux or an OSP
> finish. As expected there is some decline in solderability with each
stage
> of reflow but defect rates in wave soldering have in general been kept
within
> acceptable limits by fine tuning process parameters along the lines now
well
> established for lead-free wave soldering, i.e. close control of process
> parameters like preheat, solder temperatures and conveyor speed, wave
> dynamics that ensure good heat transfer to the board and components,
slightly
> longer contact times (~4 seconds) and, for plated through hole filling,
> slightly slower conveyor speeds and/or the use of a first turbulent wave
even
> if there are no surface mount components on the underside of the board.
In
> some cases consideration has been given to relaxation of the requirements
for
> topside fillet formation where this will not affect the integrity of the
> circuit but in general acceptable topside fillets can be achieved. A
point
> that has to be acknowledged, however, is that the fluxes used have
generally
> been the higher solids content (12-15%) resin-based (but still no-clean)
> type that have remained popular in Japan. These results might be
difficult
> to achieve with the very low solids (3% or less) "no-residue" type fluxes
> that have been popular outside Japan but the indications are that they are
> achievable with the medium solids (~5%) resin-containing fluxes that are
now
> fairly widely used in Europe and America, provided they are of the
"sustained
> activity" type, i.e. with activators that can survive the higher preheats
> (130 C) required for through-hole boards and slightly longer contact
times.
> Solder bath temperatures usually do not exceed 255 C.
>
> Good luck with your lead-free wave soldering project.
>
> Regards
> Keith Sweatman
> Nihon Superior Co Ltd
>
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the BODY (NOT the subject field): SIGNOFF Leadfree
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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
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