The BGA device side may have low area of contact due to geometry, and large
grain size (reflowed more than once = ball formation and assembly attach).
Plus excessive substrate gold or immersion gold black pad may result either
intermetallic formation (brittle) or poor interface (weak). My 2cents: (1)
get a good vendor for the substrate (no black pad). (2) and/or use thin good
quality gold (flash gold) (3) license Motorola patent (can't remember the
number) to form a dam around the interface using thick solder mask, to force
the fracture side at middle (fattest ball diameter area).... If you got easy
fracture BGA (cheap, no qual, no licensing, etc)... do not use on wireless
gadgets, like cell phone. it get drop a lot...(some blame goes to the
design, slippy design, really. another story)
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Victor G. Hernandez
Sent: Monday, June 13, 2005 3:16 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Intermittent Saga, part 2
You state to look for Au cyanide etching in the eless Ni. With what
instrument or is this under a high power micro scope (1000X). Can you
describe what to look for or perhaps you can share a photo of the
artifact you are suggesting.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leo Higgins
Sent: Monday, June 13, 2005 1:39 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Intermittent Saga, part 2
Excessive stress from pneumatic presses used to bond heat sinks to BGAs
after board level assembly has been shown to induce failure at the
solder to
BGA pad on packages that meet pre-SMT assembly quality specs in all
ways.
Subsequent analyses may show no evidence of black pad (cross sectioning
to
look for Au cyanide etching into the eless Ni, etc.).
Best regards,
Leo
Director of Applications Engineering
ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, Texas 78704
ph 512-383-4593
fx 512-383-1590
[log in to unmask]
www.asat.com
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jana Carraway
Sent: Monday, June 13, 2005 1:01 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Intermittent Saga, part 2
Werner,
If it's black pad on the component side, how would Kerry prove or
disprove
it? Could he find the cause by using Auger or cross-section? What
would be
the appropriate tests to perform to find root cause? Should he send a
component back to the supplier for root cause analysis?
Thank you,
Jana Carraway
Jana Carraway
MSEI - Advanced Technology Group
6024 S.W. Jean Road
Lake Oswego, OR 97035
503.697.5291, ext 1180
email: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier
Sent: Monday, June 13, 2005 10:04 AM
To: [log in to unmask]
Subject: Re: [TN] BGA Intermittent Saga, part 2
Hi Kerry,
You most likely have 'Black Pad' on the componet side. That, together
with
the stess concentration from the SMD-geometry, caused a briitle
ionterfacial
overstress failure.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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