Contact the Indium Corporation. They deal with many LMP solder alloys
and I suspect would have some good information/thoughts on this topic.
Rich K / GTS
847-621-7310
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Timothy McGrady
Sent: Friday, November 24, 2006 7:42 AM
To: [log in to unmask]
Subject: [LF] Low Melting Point over High Melting Point solders
I am not an expert in solder applications, so I thought I'd send this
request to the forum for discussion:
I have one small question to pose:- We are making multi layer ceramic
EMI
Filter . We are using HMP solder for making contact with disoidal
capacitor
which is under exemption but over it we are doing one dip of lmp solder
. Is
it ok to use lmp solder over Hmp solder as mother guidelines clause no7
suggest any solder will be ok with HMp solder. We are at crossroads and
got
stuck up at this point .Pl give us some clear insight and guidelines
over
it.
----- Original Message -----
From: "Werner Engelmaier" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, November 22, 2006 5:26 PM
Subject: Re: [LF] SnPb attachment of SAC BGAs
> Hi Gordon,
> As I have said in another e-mail, we need to be specific about what we
are
> talking about. what can be done in a lab under controlled conditions
is
> not an
> indication of what is possible in production.
> For a 'reflow' process the time parameter is fixed by the belt speed
which
> in
> turn is fixed by the required through-put.
> Sure, you can solder just above Liquidus, but in order to assure that
> enough
> heat is delivered, you you need to crank up the peak temperature in a
> 'reflow'
> process.
> For the typical through-put in a reflow oven, you need to reach
Liquidus
> +20C
> for about 3 to 5 seconds at THE ONE solder joint in the whole assembly
> that
> heats up the slowest [typically the center-SJ of the largest BGA].
> What most people do not realise is it is conduction heat transfer
through
> the
> PCB that heats the center-SJ of any BGA, and it is the solder paste
that
> reaches its Liquidus long before the BGA ball.
> Sure, for SnPb solder paste you can make a metallurical contact at
> somewhat
> lower T's than for SAC-paste, howerver you get very odd localized
> compositions
> as Dave hillman has demonstrated in his experiments that have been
> published.
> Indeed, the Pb-ban of this EU-RoHS directive has resulted in a big
mess,
> and
> there is no easy way around it.
> Unfortunately, I do not have a company paying my way, otherwise I
would be
> there.
>
> Werner
>
>
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