And to go back to the original question, the same principles are true for selective solder dwell times and temperatures as they are for reflow.
If a nickel barrier exists, a slightly longer dwell time in the liquid solder may be required to achieve a good IMF with the nickel, but if you attempt to use the same selective solder profile on a board with Immersion Tin as a final finish, the copper dissolution will be greater as there is no nickel barrier.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Thursday, November 10, 2016 2:57 PM
To: [log in to unmask]
Subject: Re: [TN] Reflow Profile using HASL or ENIG
Hi Vlad - If I care about the interface being formed between the solder and the board pad, I do care about the dissolution rates and their impact on the IMC formation. I wasn't talking about metal dissolution to the point of pad destruction, I was talking about the formation of IMC layer itself.
Copper/tin IMC is inherently better than nickel/tin due to crystallographic details. Does that IMC difference have an impact on solder joint integrity in many product applications? No, but it doesn't mean I should'nt pay attention to it and understand it so when it does matter I don't neglect it. And yep, I keep an eye on Alloy 42/Kovar for the same reason. And I don't need to do a ton of changes for the reflow profiles because of the plating but we do stay knowledgeable.
Dave
On Thu, Nov 10, 2016 at 2:29 PM, Vladimir <[log in to unmask]>
wrote:
> Hi Dave,
>
> You know that difference in the dissolution rates of Cu and Ni
> shouldn't even be considered. Following that path, what would one
> recommend for soldering to alloy 42 :-).
>
> Regards,
>
> Vladimir
>
> Sent from my BlackBerry 10 smartphon!e on the Rogers network.
> Original Message
> From: David Hillman
> Sent: Thursday, November 10, 2016 14:50
> To: [log in to unmask]
> Reply To: TechNet E-Mail Forum
> Subject: Re: [TN] Reflow Profile using HASL or ENIG
>
> Hi folks - lots of good comments, just one more to add: copper
> diffuses faster than nickel so some folks increase their reflow
> temperatures 5-10C and/or slow down the belt speed 3-6 inches per
> minute. It isn't necessary to do this but it does have some good
> metallurgical basis. Werner Englemaier used to advocate doing this
> when a board finish involved nickel (Werner and I discussed this at
> length, very fun conversations). I set my reflow profile based on the
> board thermal characteristics and the solder paste material but being
> aware of the plating metallurgy impacts (such as the gold embrittlement Wayne detailed) is always a good idea.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
> On Thu, Nov 10, 2016 at 1:33 PM, Jose A Rios <[log in to unmask]> wrote:
>
> > The reflow profile is typically not a function of the final finish
> > of the pwb. If it is thats news to me.
> >
> > José (Joey) Ríos, Sr QA Engineer
> > Mission Assurance
> > Kavli Institute for Astrophysics & Space Research Massachusetts
> > Institute of Technology [log in to unmask] <mailto:[log in to unmask]>
> > (617)324-6272
> >
> >
> >
> > > On Nov 10, 2016, at 2:17 PM, Wayne Thayer - EXT <
> [log in to unmask]>
> > wrote:
> > >
> > > Those two finishes are fairly similar from a wettability
> > > perspective,
> > assuming the ENIG is done properly and that no contamination or
> significant
> > oxidation occurs.
> > >
> > > If you are putting down some high-Au parts, such as leadless
> > > ceramic
> > packages, then the reduction in solder volume will make joint
> > embrittlement/stalled flow (due to AuSn being formed) more likely,
> > so you may want to adjust stencil apertures if you have those parts.
> > >
> > > But profile should probably be good. Might be able to reduce time
> > > above
> > liquidus slightly to reflect the fact that with ENIG there is no
> > oxide to strip.
> > >
> > > Wayne
> > >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
> > > Sent: Thursday, November 10, 2016 11:01 AM
> > > To: [log in to unmask]
> > > Subject: [TN] Reflow Profile using HASL or ENIG
> > >
> > > Hi Technetters,
> > >
> > > Would a reflow profile need to change based upon the finish of the
> > board? If we switch from HASL to ENIG would we need to change any
> > parameters? (I know, probably too broad of a question)
> > >
> > > Thanks!
> > >
> > > Blair
> >
>
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