I agree with Bob,
Issue is not cosmetic, the issue is quality, reliability (passing HASS,
HALT, Burn In etc.). The same appearance we be received after wave
soldering with the above alloy and the inspectors should be trained
accordingly.
The same argues I remember at 1992 during my changing to no clean process,
the PCBs were not so clean as before, so what?
I think HASL is still a PCBs finish alternative also for LF.
Best Regards
Reuven
Bob Willis
<[log in to unmask] To: [log in to unmask]
O.UK> cc:
Sent by: Subject: Re: [LF] Sn-3Ag-0.5Cu
Leadfree
<[log in to unmask]
G>
27/08/2003 18:23
Please respond
to "(Leadfree
Electronics
Assembly
Forum)"; Please
respond to Bob
Willis
It is true that some of the early lead-free solder levelled boards using
tin/copper and even tin/silver/copper were ugly, as you say and I would
never have bothered adding paste to them. I remmember the very first Lead
Free Seminar the SMART Group ran in 1999. On company handed round a
lead-free solder levelled board and I wondered why, it was very ugley.
I have to say that the quality of the levelled boards I have used have been
very good and most engineers would be hard pressed to tell the difference
between tin/lead and lead-free. As I suggested earlier the key issue is
setting up the levelling system. It takes time per design to get a good
acceptable performance. Unfortunately the industry does not want to pay any
more money for boards. Paul W at CEMCO has a good paper on solder
levelling,
its long, but the real world.
There are still issues over the pad finish thickness varaition but what I
have seen is good, and as someone once said Nothing Solders like Solder!!
I know the issue of cosmetics as well, we waste a lot of money junking good
product for cosmetic defects. In the case that you highlight of rejected
product the companies obviously did not train their staff on acceptance
criteria. All alternative finishes look different depending on process
used,
gold can vary, silver boards can look like tin, copper OSP is down to the
surface preparation.
Unfortunately some solder levelling from some producers is very poor. I
recently had levelled boards from the Far East which were actually causing
joint failures due to poor control of the alloy in the bath.
Just a few words on the subject, sorry!
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA
Tel: 01245 351502
Fax: 01245 496123
Mobile: 07860 775858
Email: [log in to unmask]
Web: www.leadfreesoldering.com
Web: www.bobwillis.co.uk
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Edward Szpruch
Sent: 27 August 2003 16:56
To: [log in to unmask]
Subject: Re: [LF] Sn-3Ag-0.5Cu
Keith,
Few comments as PCB manufacturer :
I tested some of alloye and possible applications by HASL equipment ( both
horizontal and vertical).
1) First of all, there is visual problem.Most of PCB users , especially
assembly people, are testing incoming boards just by visual inspection and
they are used to nice and shiny 37/63 solder. Lead-free solders applied by
HASL look completly different, whole range of shades, not shiny - most of
them just "ugly" . Some assembly shops rejected lead-free finished boards
just based on their appearance.
2) HASL pots are absorbing organic impurities ( fluxes resisues, solder
mask
residues etc ) and also metal contaminations - mainly copper ( dissolved in
the solder ) , oxides and some gold . All those are driving the composition
out of eutectic point . Treatment of 37/63 solder is well established while
treatment of "lead free" solders seems to be more complicated.
Edward
Edward Szpruch
Eltek Ltd
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: г аевеси 27 2003 16:33
> To: [log in to unmask]
> Subject: Re: [LF] Sn-3Ag-0.5Cu
>
> Although the holders of the Japanese patent for the Sn-3.0Ag-0.5Cu alloy
> have managed to get the Japanese Electronics & Information Technology
> Association (JEITA) to endorse this alloy as the default lead-free solder
> the reports that we have are that it does not work particularly well in
> the long term in the hot air solder levelling process (HASL). If
anyone
> has information on its successful long term use in the HASL process I am
> sure that subscribers to this forum would be interested to see it.
>
> As has been pointed out, HASL is not such a widely used printed circuit
> board finish in Japan as it has been in the US and Europe. "Prefluxes"
> and "Organic Solderability Protectants (OSP) have been more popular,
> possibly because most boards are soldered soon after manufacture so a
long
> solderable shelf life is not required. Thus, although Japan is the
> acknowledged leader in the introduction of lead-free technology there may
> not have been a strong incentive to prove up a lead-free HASL process.
>
> As I mentioned in an earlier contribution to this forum, our only
> experience of lead-free HASL has been with the Ni-stabilised Sn-0.7Cu
> alloy, which has been in use in commercial production at several sites in
> Europe for about a year.
>
> While everyone acknowledges the limitations of the HASL finish referred
to
> by other contributors to this forum it seems that it will retain a place
> in the lead-free era for the reason that made it so popular in the
> tin-lead era- the long solderable shelf life it can provide. And the
> printing and co-planarity problems that can occur because of the
"mushroom
> cap" profile it tends to leave on pads can be managed to some extent by
> good process design and control. Companies who make equipment for the
> HASL process may wish to contribute to this forum on that point.
>
> Keith Sweatman
> Nihon Superior Co Ltd
>
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