Hi Joe,

This was an automotive electronic control unit that is mounted in the
engine compartment, so yes, it did indeed see lots of wide thermal
excursions.

We haven't tried adding that variable to our re-creations, but I'm
pretty certain you're correct in your message below.

The part must have been working properly when it left our facility.  We
have three different electrical testing operations that will fail a unit
when a crystal doesn't oscillate.

I suppose we did damage the component during our repair, and the damage
continued to propagate as the unit saw use.

Thanks for your note.  I'm thinking failure analysis is at least your
second area of expertise!

Leland

-----Original Message-----
From: Joe Russeau [mailto:[log in to unmask]] 
Sent: Thursday, April 24, 2008 2:15 PM
To: TechNet E-Mail Forum; Leland Woodall
Subject: Re: [TN] Crystal Damage Question - Failure Mode

Hi Leland,

First off this is not my area of expertise.  However, you mentioned in
your 
original post that this was  a field return.  Now, that being said, I
don't 
recall anything about the end use environmental conditions being
mentioned. 
So we don't know if this product was in a controlled or uncontrolled 
environment.  Therefore, is it possible that the combination of
excessive 
heat by rework may have been the mechanism to initiate the failure and
the 
environment exacerbated the problem? Or is this a product that gets
powered 
on and off regularly, where heating up and cooling off stressed the part

resulting in the problem?  The only reason that I ask is that you
mention 
trying to recreate the issue, but you only mention in your other posts 
recreating the thermal exposure of the part.  Seems to me that if the 
product made it into the field that there could be other factors that 
contributed and if you are only recreating one factor you may never 
reproduce the problem. Like I said, I'm not an expert in this area
and/or 
perhaps I've just missed something along the way.   Just my 2 cents.

Best Regards,

Joe Russeau
Precision Analytical Laboratory, Inc.

----- Original Message ----- 
From: "Leland Woodall" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, April 24, 2008 1:31 PM
Subject: Re: [TN] Crystal Damage Question - Failure Mode


Joyce,

Our standard repair process has been to utilize a soldering iron temp at
370 degrees C, with a maximum exposure time of 5 seconds.  We've
probably repaired thousands at these settings, and this particular case
was the first time we've seen a resultant depolarization condition (one
which, by the way, we just can't seem to re-create).

It seems kinda funny that now, all of a sudden, we're having to change
our process for one single component...  I guess we'll also need to go
back and research a lot of other components to make certain we're
operating within their suggested parameters.

I assumed (yeah, I know that's a bad thing) that our parent facility had
already done this.

Oh well, guess you learn something new every day!

Thanks for your input,

Leland

-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Thursday, April 24, 2008 12:00 PM
To: TechNet E-Mail Forum; Leland Woodall
Subject: RE: [TN] Crystal Damage Question - Failure Mode

Any particular reason you have to beyond the recommended temp?
Normally, you try to stay within, or if not below the max temp. to avoid
any damage.  Single crystal at thermal shock temperature may result
excessive dislocation network that can impact quality and reliability of
the device.  In addition, the combination of stress and temp may cause
damage.  As for standard repair process: Is it the same process you have
used for this particular vendor part?  If it is not, the "standard" does
not apply to this part.  If it is just this particular batch got this
problem, your vendor is the one to blame... (the quality of the part is
not the same as per your early design qualification).
           My almost 2 cents..jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Thursday, April 24, 2008 10:41 AM
To: [log in to unmask]
Subject: Re: [TN] Crystal Damage Question - Failure Mode

Murata has not provided us with that bit of information.  They will only
tell us that we're not to exceed 275 degrees C for a maximum of 4
seconds.

We've ran experiments at much higher temps and exposure times and have
yet to destroy a component.  That's why it's so hard for me to believe
that our standard repair process is responsible for the failure...

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Honsowetz, Eric
Sent: Thursday, April 24, 2008 10:13 AM
To: [log in to unmask]
Subject: Re: [TN] Crystal Damage Question - Failure Mode

Just wondering what temperature would the crystal withstand before it
depolarized...?  Perhaps Murata could provide this information.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, April 22, 2008 1:50 PM
To: [log in to unmask]
Subject: Re: [TN] Crystal Damage Question - Failure Mode

If the original rework was due to an electrical test failure such as
would be seen if some other component failed, the crystal may have been
electrically overstressed. In that case, the assembly may still contain
the issue that caused this to happen. The rework may have been
incidental, but possibly the voltage or current overstress is what
caused the original component to fail, not necessarily the heat from the
rework. You may wish to check the assembly to see if a wrong value cap
or resistor was installed in the same (driver) circuit as the crystal
location that was replaced and failed again.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, April 22, 2008 12:26 PM
To: [log in to unmask]
Subject: Re: [TN] Crystal Damage Question - Failure Mode

Folks,

I just went over the vendor's analysis report.  In it, we were told
that:

"The crystal failed to oscillate in the initial check.  The
impedance-phase characteristics were checked, and we confirmed the
impedance response was small due to the anti-resonant point being close
to the resonant point.  We confirmed that the piezoelectric
characteristics became bad, and such were caused by depolarization.
This can be caused by the application of excessive heat.  Had this
condition been present before shipment, our electrical characteristics
sorting process would have been rejected this component, so we think the
failure was caused after shipping from Murata."

That's all the info I have.

Thanks again for your help.

Leland


-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Tuesday, April 22, 2008 12:26 PM
To: TechNet E-Mail Forum; Leland Woodall
Subject: RE: [TN] Crystal Damage Question

Was the crystal open, exhibiting wrong frequency, shorted, or what? Was
there any test analysis/troubleshooting data?
We need that in order to hazard a guess as to how the rework may have
affected the part or suggest a failure analysis strategy.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, April 22, 2008 10:16 AM
To: [log in to unmask]
Subject: [TN] Crystal Damage Question

Technetters,

We recently had a Murata SMD crystal to cause a failure in the field.
This particular unit had been to Repair and the component was manually
replaced during the manufacturing process.

The vendor analysis reported the component saw excessive heat during the
rework and caused internal depolarization which led to failure.

We made 10 attempts to re-create this condition and were unsuccessful in
doing so.  We used dual soldering irons, had the temps cranked as far as
they would go, and gave them excessive exposure times.

Could the vendor analysis have been incorrect, or was their explanation
a real possibility?

Why were we not able to replicate this?

Thanks in advance,

Leland

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