Yes that's an excellent idea. Making two halves of the joint separately and
then melting together is a good tip for any difficult soldering operation.
You will probably also find that - providing you can do it - that very long
heating cycle at just over liquidus will achieve a normal looking solder
joint preferably with a weight to sink part (makes up for reduced flow
coherence)and inerting (the flux won't last that long). Sort of area under
the graph thing. I.e. short and high is same as long and low. Long is 10 s
of minutes. This is proven trick from long ago.
Regards
Mike
-----Original Message- ----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Tuesday, November 12, 2013 6:09 PM
To: [log in to unmask]
Subject: Re: [TN] SnBi solder and SAC solder balls
Hi Guy-
I suspect your customer only wants the joints to be as reliable as if the
whole assembly was soldered with SAC305. And as long as your service
temperatures are at least 40C below the melt, the SnBi should be able to
meet this bar. On the other hand, if you were to switch to SnPb, then the
customer might demand a higher bar!
By the way, I've found that pre-flowed solder, such as the product SIPAD
puts out, allows reflow at about 10C less than with paste (much much less
surface area the flux needs to clean). You might want to consider something
like that if you need to keep SnPb below 210C.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Tuesday, November 12, 2013 12:57 PM
To: [log in to unmask]
Subject: Re: [TN] SnBi solder and SAC solder balls
Oh I been Googling!
The long and short of it is, no-one can know without understanding the whole
solder system.
My gut tells me the result wouldn't be unreliable in an environment with
thermal excursions below 100C, and service life less than 5 years, but
Murphy was an optimist.
The solder charge combination of SAC38 from Samtec's part and the mix of
SnBi solder paste, with process variation during reflow, make a very complex
and difficult system to optimize and model. Better to stay SnPb and order
the part with SnPb solder charge.
Some of the aging properties of SAC305 are a little frightening for long
service products.
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Monday, November 11, 2013 6:15 PM
To: [log in to unmask]
Subject: Re: [TN] SnBi solder and SAC solder balls
I remember something about internal oxidation SAC plus Bi. Can't remember
exactly what impact on reliability. You might want to goggle it.
Original Message
From: Mike Fenner
Sent: Monday, November 11, 2013 5:26 PM
To: [log in to unmask]
Reply To: [log in to unmask]
Subject: Re: [TN] SnBi solder and SAC solder balls
Guy
To address your last question first: No I don't believe that mixing Sn/Ag/Cu
with Bi/Sn will produce the possibility of a reduced melting temperature
intermetallic zone forming in your solder joints analogous to those reported
when mixing Sn/Pb with SAC. (Sn/Pb/Bi MP around 100C). The lowest melting
range combination pair of constituents is already present (Sn/Bi at 138C).
For your other queries: Welcome to Conjecture World!
We can note
1) That the properties of Sn/Bi have been found to be improved by the
addition of silver.
2) That "reinforced SAC" or "enhanced SAC" alloys have been developed by the
addition of small alloying additions of Bismuth and other stuff.
Patented alloys which have enhanced thermal cycling abilities, temp
withstand etc from these additions are available from certain suppliers, and
are reasonably well documented and have been in use in high rel apps (auto
etc) for some years.
So that sounds kind of favourable. what will actually happen will depend on
the actual alloy mix you form, how homogenous it is, the stresses that the
assembly will see in service and the service life you are looking for. You
might be able to puzzle something out from phase diagrams but you have a lot
of variables, I can understand binary diagrams,(2D) and cope with ternary
(3D) but I can't do 4D or more. Not many people can - do four dimensions
that is. You need a proper metallurgist or to talk to someone who has gone
before you. In that respect I did get the link in the NASA report given by
Dave to work by a little jiggery pokery (it doesn't seem to work direct). I
did a quick scan through. It's longer than I can cope with at this time of
night, but it looks as though it might be helpful.
It's below
https://tdglobal.ksc.nasa.gov/servlet/sm.web.Fetch/TEERM_LFE_JTR_FINAL.pdf?r
hid=1000&did=41742&type=released
Sorry not to be more specific, maybe others with more direct experience can
be more helpful.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Monday, November 11, 2013 1:30 PM
To: [log in to unmask]
Subject: Re: [TN] SnBi solder and SAC solder balls
Hi Guy - The NASA DoD Lead-free Project did test SAC solders with SnBi
surface finishes so that information may be helpful (not exactly what you
are looking for). The project results can be found on at:
http://www.teerm.nasa.gov/NASA_DODLeadFreeElectronics_Proj2.htm
Honeywell and Celestica have also published an investigation on tin/bismuth
solders - check the APEX proceedings for that information.
Dave Hillman
Rockwell Collins
[log in to unmask]
From: Guy Ramsey <[log in to unmask]>
To: <[log in to unmask]>
Date: 11/11/2013 07:19 AM
Subject: [TN] SnBi solder and SAC solder balls
Sent by: TechNet <[log in to unmask]>
We have a customer in Korea using Samtec ?Solder Charge? connectors. The
alloy is SAC38 ( 95.5, 3.8, 0.7).
They want to stay Pb-free.
Our 60 layer, 480mm by 585 mm by 6.5 mm thick board, with 6100+ embedded
capacitors cannot survive the Z axis expansion seen at SAC reflow. Test
samples have survived 10 reflows at 210°C.
Has anyone tried to qualify the performance of SAC solder with SnBi solder
paste? Does it have the same problems associated with mixing SAC and SnPb
paste?
Thanks,
Guy
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------------------------
This transmission (including any attachments) may contain confidential
information, privileged material (including material protected by the
solicitor-client or other applicable privileges), or constitute non-public
information. Any use of this information by anyone other than the intended
recipient is prohibited. If you have received this transmission in error,
please immediately reply to the sender and delete this information from your
system. Use, dissemination, distribution, or reproduction of this
transmission by unintended recipients is not authorized and may be unlawful.
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
|
