Hi Paul
Thanks a lot for your important insights
We checked the base materials issue.
This is the same material we used for a long time and the same thermal
stress
Never before we got those cracks,
Any other inputs will be great,
Thanks again,
Ido Mashall
Fax: +972-4-6376666, Tel: +972-77-2127172,
Mobile +972-52-5901114, www.beyond-materials.com
-----Original Message-----
From: Paul Reid [mailto:[log in to unmask]]
Sent: Sunday, October 05, 2008 1:28 AM
To: TechNet E-Mail Forum; Ido Mashall
Subject: RE: [TN] Barrel and Corner cracks in copper elctroplating
Hi Ido,
I am responding from a reliability, rather than a QC/QA, point of view.
Therefore I will not be commenting on whether this passes or fails to meet a
requirement.
I have reviewed the photos and what I noticed is that the cracks in the
barrel are more or less horizontal and proceed through copper crystals (as
opposed to going around copper crystals). I also noticed that the cracks are
open at ambient. There is no obvious smoking gun here; the copper looks well
plated with good distribution and the material is not significantly degraded
(i.e. no delamination, crazing) based on visual examination. It does not
appear that the electrolytic copper has a columnar crystal structure,
burning or nodulation all of which would suggest a copper plating problem.
I would say that this is a typical failure mode created by high temperature
thermal excursions. The barrel cracks associated with temperatures greater
than 230°C frequently present in this manor. We see this failure mode
frequently in lead/free assembly and rework typically at 260°C.
Since you floated the specimen at 288°C this is the expected failure mode if
the barrel is going to fail. My visceral reaction is that the material is
playing a role in this failure. Notice that there is pad rotation exhibited
by some of the inner layers. The material has undergone Z axis expansion and
has begun to degrade as demonstrated by the plastic deformation visible in
the section (open crack). If the dielectric were not adversely affected by
the thermal excursion we would expect the material to retain its' elasticity
and the crack to be closed at ambient (self healing). What we see in this
section is a reluctance to return to the original shape (physical
hysteresis). Electrically the circuit would have exhibited an irreversible
increase in resistance (electrical hysteresis). Also there appears to be
some degree of copper thinning or deformation at the facture sites that
suggests significant strain to the PTH. Most would say that the CTE is the
major factor for this deformation but I am beginning to believe it is
function of CTE and viscosity (material stiffness) that work in concert to
increase the stress in the copper barrel.
I would say that this is a high temperature barrel crack type failure and
the material is playing a significant role.
Reliability at higher temperatures is a synergistic relation between copper
quality, material robustness, and PWB design (layout and build). I believe
this failure is a sum total of the influence of those three factors.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ido Mashall
Sent: Friday, October 03, 2008 2:13 PM
To: [log in to unmask]
Subject: [TN] Barrel and Corner cracks in copper elctroplating
Hello technet
We are suffering a serious problem of barrel and corner cracks in the
pattern copper plate bath.
Please look at the following pic. (all after 288C solder thermal stress)
http://www.drivehq.com/file/df.aspx/shareID4765976/fileID233954134/eo-d3497-
1.jpg
http://www.drivehq.com/file/df.aspx/shareID4765976/fileID233954135/es-c9633-
1.jpg
http://www.drivehq.com/file/df.aspx/shareID4765976/fileID233954138/as-d3715.
jpg
This very strange phenomenon occurs only in the second copper, and does not
occur in the panel plated copper.
After testing all bath components, they seem to be ok. CVS is oK, hull cell
is OK. It seems the copper lost its mechanical properties.
We are looking for possible contamination and changed the bath for a new
fresh bath, and it happens again after a few days..
Does somebody have some idea why this cracks can occur? What other
reasons..?
Thanks.
Ido Mashall
Fax: +972-4-6376666, Tel: +972-77-2127172,
Mobile +972-52-5901114, http://www.beyond-materials.com/index-en.htm
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