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A Novel Green Technology for the Plated Through Hole Process
Electroless copper has long been the dominate process for plated
through hole (PTH) metallization. The technology is widely used by
printed circuit board fabricators and driven by a long standing
acceptance by OEMs. However, this established technology has many
drawbacks that have a direct impact on our environment. Namely, it
contains a known carcinogen, consumes a lot of water and is inherently
unstable leading to increased demands on waste treatment operations.
Through the years there has been significant work done in this area of
the manufacturing process to overcome the challenges associated with
electroless copper technologies. The ultimate goal being an
environmentally friendly PTH process that maintains well established
performance and reliability standards.
by Ying (Judy) Ding
Richard Retallick
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The Path to Robust Electronics - Preventing Corrosion of PCB Assemblies
All things corrode, and the rate of corrosion among electronics devices is accelerating. Electronic devices are being used in more places than ever before. They are finding more uses, they're more portable, and they're increasingly used in polluted areas. Worldwide industrialization has produced more sulfur, chlorine and nitrogen compounds that aggressively attack electronics. The initiatives to eliminate lead (Pb) in electronics reduced the ability for circuitry to resist corrosion. To replace thick tin-lead deposits more circuits employ thin, easily corroded surface finishes on the PCB, connectors, and component leads. There is a need for better prediction of service-life corrosion, yet there is a lack of adequate test methods. Environmental testing rarely progresses beyond thermal cycling or heat/humidity. Mixed flowing gas testing uses standardized pollutants as a stress to electronics, but has limited success in reproducing all corrosion failures. An elevated rate in the observation of one type of failure, termed creeping corrosion, motivated the electronics industry to review corrosion test methods. As part of the IPC 3-11g committee, a number of OEM's, EMS providers, PCB fabricators, material suppliers, universities, and testing laboratories joined forces to address the need for better corrosion prediction.
by Don Cullen
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Effects of Adhesion Promotion Treatment on Electrical Signal Attenuation
As the electronics industry transitions to lead free assembly, PCBs
will need to endure increased mechanical stresses due to the elevated
reflow temperatures of Pb-free solders. This inherent change in process
parameters has led some companies to examine the reliability
relationship between laminate pre-preg and oxide alternative. It is
important to note that historically it was assumed that “rougher
isbetter” when it came to adhesive bond promotion. The thought being
that the more surface roughness on the copper surfaces the better
adhesion will be. In some cases this is true. In many other cases,
however, rougher copper is not necessarily a prerequisite for good
adhesion and may actually have a deleterious effect on electrical
signals.
by Roger Krabbenhoft
Bruce Lee
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Verifying Microvoid Elimination and Prevention Via an Optimized Immersion Silver Process
The Pb-free transition in the electronics industry has seen immersion
silver emerge as a leading circuit board finish for RoHS compliant
processes and products. It is utilized in a wide crosssection of
end-use applications, both simple and technically sophisticated. The
strengths of immersion silver are numerous; process simplicity at the
fabrication level, contact functionality,and durability to multiple
reflow cycles are some of the most noteworthy. Recently, the subject of
solderjoint microvoiding has been linked to immersion silver
processing, and studies of this phenomena have found microvoiding to
present unacceptable risk to the reliability of electronic goods. This
work is a continuation of previous publications which explained key
root causes of microvoids, along with effective steps at preventing
them. The work below presents a review of past findings, additional
data confirming the proposed microvoid mechanism, and a substantial
volume of production verification data. A direct comparison of this
optimized process to an alternative immersion silver chemistry is also
given.
by Don Cullen
John Swanson
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Creeping Corrosion of PWB Surfaces in Harsh Sulfur containing Environments
A failure mechanism known as creep corrosion has been gaining the
attention of the electronics industry over the past year. Industry
committees have formed to decide which paths are best taken to
identify, recreate and eliminate this corrosion process. Though some
key elements such as the presence of sulfur and high humidity have been
identified as triggers for producing this defect type, the true
mechanism and physical nature by which this mass transport controlled
process occurs is not fully understood.
by Dr. Ernest Long
Lenora Toscano
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Characterization, Reproduction, and Resolution of Solderjoint Microvoiding
Microvoids are tiny voids in solderjoints and differ from more well
known solderjoint voiding in their individual size and location. The
microvoids discussed herein are described as an abundance of small
voids at or near the interface of a PCBA solderjoint. In the most
severe cases, a solderjoint my fail physically and electrically. Each
void reduces the cross-sectional area of the solderjoint; at some point
the remaining solder is insufficient to meet functional demands. While
information related to these tiny interfacial voids has existed in
industry literature for several years, the use of recently available
X-ray analytical equipment has raised the level of microvoid
observation. It is not known if microvoiding is responsible for
previously failed assemblies to which no root cause failure mode had
been assigned. Unlike “Black Pad” interfacial fractures related to
Electroless Nickel Immersion Gold, microvoiding has not been directly
related to a galvanic effect of PCB circuit design. This provides hope
that the phenomenon may be more easily prevented, even on the most
difficult designs.
by Donald P. Cullen
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"Behind the Scenes" of Effective OSP Protection in Pb-free Processing
Advancements and evolutions in printed circuit board manufacturing, design, and electronics assembly have driven new research on high temperature organic solderability preservative (HT OSP) surface finishes. More specifically, developments in OSP chemical processes are aimed at producing adurable finish which ensures that a board surface retains solderability through more challenging and harsh Pb-free assembly conditions. From this, it is clear that advancements in OSP processing and coating performance require a solid understanding of the mechanisms associated with coating formation and thermally driven degradation. This work examines and describes OSP structure and composition and how it is affected by heat treatments. Additionally, mechanisms of degradation of OSP are proposed along with possible strategies to remedy it.
by Dr. Jun Nable
Dr. Witold Paw
John Swanson
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Increasing IC Leadframe Package Reliability
As the conversion of the electronics industry to lead free soldering
materials continues some unexpected negative side effects of higher
lead free reflow temperatures have occurred. Component level defects
such as delamination and “popcorning” in surface mount IC lead frame
components have increased significantly since lead free soldering has
become mainstream.
by John Ganjei
Dan Hart
Bruce Lee
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Cupric Chloride-Hydrochloric Acid Microetch Roughening Process and its Applications
MultiPrep is a cupric chloride-hydrochloric acid based microetchant process developed by MacDermid, Inc. based in Waterbury, CT. This process provides a unique roughened copper surface, which yields excellent adhesion for both solder mask and dry film photo resist applications. The process also yields excellent solder mask adhesion through subsequent silver, tin and nickel plating post solder mask application.
by Steve Castaldi
Kesheng Feng
Brian Jobson
Nilesh Kapadia
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