you may want pay Calce for details.
"Hollow Fibers and Conductive Filament Formation
Increases in failures due to internal board shorting by conductive filament
formation (CFF) have driven glass and laminate manufacturers to consider
screens and qualification tests to assess the hollow fiber concentration of
circuit cards.
Laminates composed of hollow fibers pose a threat to the reliability of
electronic systems in that they provide a convenient open path for CFF. CFF,
also referred to as metallic electromigration, is an electrochemical
process. This process requires, as do all other migration phenomena, the
transport of a metal through or across a nonmetallic medium under the
influence of an applied electric field. CFF is difficult to detect in the
field because once it occurs, sufficient heat is generated to "vaporize" the
conductive filament and "clear" the failure. Furthermore, observation of a
partial filament requires destructive analysis. The most apparent solution
for the elimination of hollow fibers is to improve manufacturing processes
and controls.
Multi-layer organic laminates, which make up over 90 percent of the present
types of interconnecting substrates in today's electronics (standard FR-4
represents 85 percent of resin systems), can develop a loss of insulation
resistance between two biased conductors due to the CFF phenomenon. The
opportunity for failure due to CFF is a function of temperature, moisture
content, the voltage bias, and manufacturing conditions.
E-SEM Image of a Hollow Fiber
Based on CALCE EPSC's recommendations, hollow fiber assessment has now
become a standard screen by some board fabricators and contract assemblers
to qualify suppliers and discard lots with hollow fiber concentrations above
specifications. The CALCE EPSC specification being used by laminate
manufacturers for this screen is no more than one hollow fiber per 10 cm x
10 cm. This guideline specification reduces the CFF opportunity to less than
1 percent, based on calculations done at CALCE EPSC. As a result of CALCE
EPSC's efforts, Nan Ya Plastics, one of the world's largest glass fiber
manufacturers, revised their glass production process and experienced a
sharp drop in hollow fiber concentration.
For more information on hollow fibers and conductive filament formation,
contact Dr. Craig Hillman or Keith Rogers at 301-405-5316. "
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Donald Vischulis
Sent: Tuesday, February 01, 2005 5:48 PM
To: [log in to unmask]
Subject: [TN] FAB Question
One of our engineers approached me about the use of hollow glass fibres in
FR-4. I've never heard of this concept before. Can anybody educate me?
This is supposedly a new development from Asia.
Don Vischulis
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