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April 2016

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Subject:
From:
Ricardo Moncaglieri <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ricardo Moncaglieri <[log in to unmask]>
Date:
Tue, 19 Apr 2016 10:30:12 -0300
Content-Type:
text/plain
Parts/Attachments:
text/plain (355 lines)
Resuming answers to several questions:
 
At this time development engineers are reconsidering
pcb-case-terminal-solder CTEs interaction.
Laboratory eng reported test cycling temperature didnt pass in no case
+125°C
 
Both pictures are from the same specimen under test. Due too solder
connection displacement when "cracking" in one of them you cann´t see
the golden surface of terminal just at the left side.
 
Degolding was done from double pre-tinned
 
Thermal cycling is: 100 cycles -50°C to +125°C . Ramp rate per each
cycle is 45´ (-50 to +125°C)
(I´m sorry for correction, engineer test laboratory at first time
reported +50°C to +125°C)
 
brgds,Ricardo

>>> George Wenger <[log in to unmask]> 19/04/2016 10:02 >>>
It also won't hurt to do an XRF measurement on the PCB surface finish
to know how thick the ImmAu and EPd were on the PCB 

----- Original Message -----

From: "David Hillman" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Tuesday, April 19, 2016 8:31:22 AM 
Subject: Re: [TN] Solder Cracking After Thermal Cicling 

Hi Richard - Ricardo had mentioned the component leads were "double
tinned" 
to remove the gold but it sure wouldn't hurt to do a simple cross
section 
to confirm that gold embrittlement wasn't playing a role in the issue
too. 

Dave 

On Tue, Apr 19, 2016 at 7:03 AM, Stadem, Richard D. < 
[log in to unmask]> wrote: 

> I agree with Dave, but with the addition that Steve may be on to
something 
> in that the "before" picture shows some gold, the "after" picture
does not, 
> so this may not be the same terminal. But that is irrelevant; what I
am 
> adding here is that the gold may be contributing to the issue as
well, in 
> the form of embrittlement. 
> 
> -----Original Message----- 
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman 
> Sent: Monday, April 18, 2016 7:25 PM 
> To: [log in to unmask] 
> Subject: Re: [TN] Solder Cracking After Thermal Cicling 
> 
> Hi folks - this case isn't as complicated as it might look. Its a
simple 
> case of CTE mismatch. The component lead is very very short with no
strain 
> relief bend. And as Joyce mentioned, the lead base metal may be 
> accelerating the solder shear forces (i.e kovar or alloy 42). Add in
the 
> influences of the board laminate, the component body construction and
the 
> solder joint volume/pad size, you end up with the result shown in the

> photos. 
> 
> Dave Hillman 
> Rockwell Collins 
> [log in to unmask] 
> 
> On Mon, Apr 18, 2016 at 5:05 PM, Ricardo Moncaglieri < 
> [log in to unmask]> wrote: 
> 
> > Jim, 
> > Temp cycle range is +50°C to +125°C. 
> > I dont have yet the temp ramp rate. 
> > brgds,Ricardo 
> > 
> > >>> "Maguire, James F" <[log in to unmask]> 18/04/2016 19:02

> > >>> 
> > What is temp cycle condition again? You have 50 to 125C but did you

> > mean -50C to +125C? Also are you doing temp cycle or air/air temp 
> > shock (ie. what is ramp rate in chamber or better yet as measured
on 
> > the product during temp cycle). 
> > 
> > 
> > Jim Maguire 
> > Intel Corporation 
> > ATD Q&R Stress Lab Operations 
> > Hawthorne Farms; Oregon 
> > Engineer 
> > Phone: 503-696-3309 
> > Cell: 253-651-9373 
> > 
> > -----Original Message----- 
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Ricardo 
> > Moncaglieri 
> > Sent: Monday, April 18, 2016 2:58 PM 
> > To: [log in to unmask] 
> > Subject: Re: [TN] Solder Cracking After Thermal Cicling 
> > 
> > Steve, 
> > Responding your question. 
> > 
> > Soldered connection is not put under vibration during temp cicling.

> > 
> > This terminal belongs to a connector which is screwed on a case and

> > its terminal passes through this metalic case and lyies on the pcb

> > ENEPIG pad. 
> > So that there are following CTEs playing and intercating each other

> > all 
> > together: 
> > 
> > PCB CTE 
> > Solder CTE 
> > Case CTE where is screwed the conector Terminal CTE 
> > 
> > brgds,Ricardo 
> > 
> > >>> Steve Gregory <[log in to unmask]> 18/04/2016 18:47 >>> 
> > Hi Ricardo, 
> > 
> > I finally have your pictures up, they are here: 
> > 
> > 
> >
http://stevezeva.homestead.com/A15_Photos_of_pre__post_100_temp_cyclin 
> > g_CSC-10_SN12.pdf 
> > 
> > Boy, that looks like a big CTE mis-match. A question; are the
boards 
> > going through ESS? Vibration along with the temp cycling? 
> > 
> > Steve 
> > 
> > On Mon, Apr 18, 2016 at 2:35 PM, Ricardo Moncaglieri < 
> > [log in to unmask]> wrote: 
> > 
> > > Steve, 
> > > Attached arethe pictures. 
> > > Thank you a lot. 
> > > Await for your comments. 
> > > brgds,Ricardo 
> > > 
> > > >>> Steve Gregory <[log in to unmask]> 18/04/2016 15:22 >>> 
> > > Hi Ricardo, 
> > > 
> > > The Technet server strips the attachments, send your photo
directly 
> > to me 
> > > and I'll get it posted... 
> > > 
> > > Steve 
> > > 
> > > On Mon, Apr 18, 2016 at 11:43 AM, Ricardo Moncaglieri < 
> > > [log in to unmask]> wrote: 
> > > 
> > > > Dear colleagues; 
> > > > 
> > > > Steve Gregory, could you please upload the enclosed picture? 
> > > > 
> > > > Solder become perturbated / cracked after thermal cicling: 
> > > > 
> > > > This picture corresponds to a plane (not circular) conector 
> > terminal 
> > > > solded to a pcb pad ENEPIG finished. 
> > > > The connector terminal has been gold removed by twice pretin. 
> > > > Solder used is Sn63Pb37. 
> > > > Thermal cicling: 50°C to 125°C 
> > > > 
> > > > As picture showed there are stretch marks toward left direction

> > and 
> > > > showed solder crack. 
> > > > 
> > > > Our provider reported temperature didnt pass over 125°C and
solder 
> > used 
> > > > 63/37. 
> > > > 
> > > > Question: 
> > > > 
> > > > How could these kind of gooves or stretch marks have been
produced 
> > 
> > > > taking into account they are just toward one direction (left)
and 
> > of 
> > > > considerable length? 
> > > > Just mecanic stress? 
> > > > Temperature overpassing on any cicle? 
> > > > Need of use of different alloy, ie.: In, Bi etc? 
> > > > Provider reported the process is being useed from them since
long 
> > ago 
> > > > (same solder alloy, temperature, pcb, terminal conector,
thermal 
> > > > cicling) but this is the first time they faced with such a 
> > cracking. 
> > > > 
> > > > Do you have any comment in order to anlyse/solve this trouble.

> > > > 
> > > > Appreciate your feedback we are in middle of a providing 
> > acceptance 
> > > > tests space quality level (IPC class 3). 
> > > > 
> > > > brgds,Ricardo 
> > > > 
> > > > 
> > > > 
> > > > 
> >
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