1. This is not correct. With the alloys and settings we have been using the
finish is bright and uniform. Interestingly the XRF measurements for a given
setting (and appearance) are better. Sounds like your supplier was not
experienced. The only significant challenge we have seen to date is that the
lower superheat demands pre heating with thick boards. Conventionally
vertical systems do not use pre heat.
2. I don't understand these comments. The dissolution rate of copper into
Tin slows down as the copper content rises. To maintain the copper
concentration below 0.3 using SnPb demands daily 'skimming' or dilution and
it is easy to overshoot the limit if daily analysis is not made. Our
experience with SnCu and SnCuNi to date is that topping up with pure Sn or
SnNi (to replace the metal transferred to the board) maintains the alloy
within specification. This seems to correlate with the experience of wave
soldering machine users I have spoken to although they do suffer tin
depletion due drossing; something that does not happen with a correctly
operated horizontal or vertical leveling system.
Organic contamination of solder is not something I have experienced in the
30+ years I have operated and manufactured Solder coating machines but it is
true that other metals readily alloy with tin but I don't see the problem
being significantly different with the lead free alloys on our HASL
equipments.
-----Original Message-----
From: Edward Szpruch [mailto:[log in to unmask]]
Sent: 27 August 2003 04:56 PM
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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