Collaborative cleaning process innovations from managing experience and learning curves
Figure 2. Cause/effect diagram for leading edge printed circuit assemblies.
 
specific studies to determine the risk of into cleaning all visible and entrapped flux The high impedance device requires all
residues under components. residues under components. flux residues removed to obtain greater
 
The move toward lead-free soldering circuit performance in order to detect
and miniaturization represent two force customer—cleaning material— heart conditions and direct therapy.
fields converging that increase no-clean cleaning equipment collaborations The problem is that denser designs use
complexities.
3
Higher lead-free melting The pace of technology development and smaller components, such as flip chip,
temperatures requires the use of fluxes innovation has changed the way customers QFNs, BGAs and small chip cap resistors/
with greater thermal stability. The problem and suppliers communicate and interact capacitors, from under which it is
is that lead-free alloys exhibit poorer on a global scale. To understand the extremely difficult to remove trapped flux
wetting properties, which require higher jobs that customers need done, suppliers residue trapped.
flux capacity and strength to improve identify customer needs that cannot be Other users presented on the risk of
wetting and flow. Flux technology also done satisfactorily with current solutions.
5
cleanliness when leaving flux residues
plays an important role in reduced voiding Working from the outside-in, companies under low-standoff components and large
by increasing the need for high oxidation who supply pieces of the process area array packages. Customers are now
resistance, oxygen barrier capability, collaborate by looking at the world from measuring and quantifying flux residues
high thermal stability and low volatility. the customer’s perspective to understand underneath site specific components on
Miniaturization requires the flux to be what the customer is trying to do and a printed circuit board, which may risk
more stable at peak reflow to prevent identify product or process characteristics electrochemical migration, leakage and
oxidation, which requires a higher content for solving the customer’s job. Starting corrosion.
7
A military subcontractor talked
of resin or rosin. Reducing flux volatility with a deep insight into the job the about the use of high impedance circuitry
has a tradeoff of greater amounts of circuit customer is trying to accomplish shifts the and their sensitivity to small levels of flux
assembly flux residue. Halide-free flux focus from solutions that customers use residue left under components.
10
Leadless
materials will require higher levels of weak to the fundamental issues the customer is chip carriers have standoff heights less
organic acids, which in turn increase the trying to solve. than 2.0 mils off the board. During the
level of ionic materials that can form an The IPC/SMTA High Performance soldering process, the surface tension of
electrochemical cell. Cleaning Symposium, held in October the flux propagates between the center of
Electrolytic corrosion, electrochemical 2008, was a user-driven conference the ground pad and power source, which
migration and electrical leakage occur comprised of OEMs, contract assemblies creates a reliability concern. Additionally,
when electronic circuits are exposed to and material supply companies. The user vias under the component entrap pockets
humid conditions (moisture), electrical presentations highlighted a number of of residue that can cause field failures.
potential (bias) and ionic residue (flux cleaning jobs that customers were trying Lower standoff heights for mounted
disassociation).
4
Figure 1 shows the failure to get done when building high reliability flip chip die result in higher I/O counts
region that illustrates the risk of voltage, conventional and leading edge printed and lower I/O pitches.
8
There are specific
humidity and ionic contamination when circuit assemblies. A medical equipment challenges created by the disruptive
they intersect. Miniaturization, high supplier noted, “Our products require influences for underfills: fluxes, flux
density and lead-free soldering trends clean circuit boards to function correctly.”
6
residues and the interaction between
raise the question of whether the failure This particular customer is building heart underfill and flux residue. The transition
region increases. To address this concern, monitors. Residues under active and to high tin, lead-free solder technology
leading edge designers are moving away passive devices can short out the device creates problems for no-clean flux residues
from no-clean soldering processes and back when exposed to humid conditions. under flip chip die. As the gap heights and
www.globalsmt.net Global SMT & Packaging – October 2009 – 25
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