At times,the electronics industry changes faster than the testing and regulatory groups serving the industry. In this case,the
electronics supply chain thoroughly evaluated the new printed circuit board (PCB) surface finish Immersion Silver. The
silver finish was subjected to comprehensive testing and received product specifications throughout all industry sectors
between 1995-2003. Specifications within Underwriters Laboratories (UL),however,were not current with the industry
testing. UL maintained concerns over the use of silver metal in electronic packages,and implemented special testing for PCB
devices using silver in their construction if the device was intended to operate at higher voltage/energy levels. UL’s concern
with the use of silver revolved around historical accounts of dendrite formation,a type of defect caused by electrochemical
migration. The UL restriction began to hinder widespread use of immersion silver by OEM’s who had conducted extensive
reliability studies. Upon review,it was determined that the UL electrochemical migration test method needed to be updated to
reflect changes in PCB technology. Further investigation proved that all surface finishes could fail the UL test method,even
if there was no evidence of dendrite formation.
A group of companies from the electronics supply chain formed a Task Group to work with UL in updating their
specifications. Later,this group became the IPC 3-11g Metal Finishes Data Acquisition Group. This article describes the
testing,demonstrations,revisions,and ongoing work of IPC 3-11g in coordination with Underwriters Laboratories. More
specifically,this article will present data from a team project to identify the important parameters affecting electrochemical
migration from the viewpoint of UL.

To meet the emerging requirement of eliminating lead from electronics,the printed wiring board (PWB) industry is migrating
from hot-air-leveled SnPb solder to alternative final finishes. A thin layer (2-3 microinches) of silver coating on copper has
proven to be solderable for up to one year,and to withstand the higher temperature excursions encountered when using lead–
free solders. A new improved process capable of a wide range of thickness is needed to meet current and future applications
beyond solderability,such as pressfit and long term contact resistance. There is a perception that silver thickness alone
determines application success. This paper describes a new immersion silver process and the resulting coating properties in
tarnish resistance,solderability,surface insulation resistance and electromigration resistance.

The influence of co-deposited Phosphorous (P) (from low to high P) within an electroless Nickel layer,regarding the
reliability of the solder joint integrity was investigated. The solder joint evaluation was carried,using solder mask defined
BGAs as test vehicle and using the ball shear technique to establish the level of any “Brittle Fracture”.
The type and structure of the IMC created before and after thermal cycling was examined against the co-deposited P (from
low to high P) within an electroless Nickel layer to determine if this has any influence on solder joint integrity.
Due to the nature of the electroless plating process,a high P-ENIG coating has a P content in the plated electroless Nickel
layer of about 9.5 to 13 wt.%. This high P content leads to an amorphous structure,with no grain boundaries,which therefore
influences the formation of the IMC between Nickel and solder. The high P content of the bulk electroless Nickel layer seems
to control the diffusion rate of the Nickel into the solder,resulting into a dense and uniform IMC formation.
This paper describes the influence of co-deposited P (from low to high P) within an electroless Nickel layer,regarding
“Brittle Fracture” and the reliability of the solder joint integrity,using solder mask defined BGAs as test vehicle.
The variation of the co-deposited P content did alter the characteristics of the ENIG surface,which impacts the yield at the
assembler. It turns out that a high P content in the bulk Nickel layer increases the reliability of the solder joint.

With the electronics industry rapidly moving to lead-free soldering and requirements for long term reliability of the assembly
becoming more critical,fabricators and OEM’s must determine the most cost effective and reliable means of achieving bare
board solderability and component attachment. OSP’s have long provided a reliable and inexpensive means of satisfying
these requirements. However,greater solderability requirements,(measured as joint strength,paste spreadability and hole fill),
and higher temperatures of lead-free soldering,have greatly diminished the use of conventional (standard substituted
benzimidazole based) OSP’s. However,with the development of third and fourth generation organic solderability
preservatives based on a novel aryl-phenyl imidazole compound,OSP has regained its leadership role as a final finish,
particularly in Asia and Europe. In addition,the technology shift to bare copper PWB’s with selectively plated gold features
is requiring OSP’s that do not tarnish or deposit on the gold. This paper will explore the development and implementation of
the next generation OSP for lead-free soldering. The OSP performance will be compared to other surface finishes (ENIG,
ImTin,Immersion Silver,conventional OSP) in terms of solder paste spreadability,solder hole fill and solder joint strength.
Reliability studies will be performed with both standard lead based solders and lead-free solders and include solderability
performance with multiple reflows and artificial aging conditions.

An Electroless Nickel and Immersion Gold (ENIG) plating process with a middle phosphorous content nickel layer is
currently a mainstream final finishing application for mobile phone Printed Wiring Boards (PWB). As a trend according to
the worldwide market growth of mobile phones,the demand for higher resistance characteristics in corrosive environments
for ENIG finished boards has increased. Although various methods have been introduced as an evaluation method for higher
corrosion resistance,sulfurous acid gas (SO2 gas) testing is a recent area of industry focus. However,because of the
significant corrosive characteristic of SO2 gas,the conventional ENIG layer cannot tolerate this testing method,and thus has
become an area of major concern. As a result,a high phosphorous nickel ENIG plating process,which inhibits higher
resistance in a corrosive environment compared to a middle phosphorous process,is being adopted as a final finishing
method. However,several other factors of the total plating process that may influence corrosion resistance have not been
verified or fully investigated. Therefore,in this study we introduce ENIG plating layer characteristics required for higher
resistance in corrosive environments by investigating corrosion conditions of ENIG layers caused by SO2 gas testing,and
furthermore conduct observations on factors that influence these ENIG characteristics.

A study was conduced to see if faster laser ablation rates,improved fracture resistance and better copper adhesion
after electroless plating could be engineered into existing Resin Coated Foils (RCF) with out diminishing any thermal,
electrical or mechanical properties -- all while staying cost competitive. That the main factors that can influence ablation rates
and fracture resistance are possibly thru base resin chemistry while the improved adhesion of electroless platted copper is
believed to be more influenced by the surface roughness and morphology of an etched circuit board.

There is continued interest in utilizing alternatives to bromine-based flame retardants for printed wiring boards. As a result,a
wide variety of phosphorus and non-phosphorus systems have been developed for various thermoset resin systems. The
development of a new type of phosphorus flame-retardant material that performs in the curing reaction of epoxy resins is
discussed in this paper. The new material is a solid that can be formulated in several common formulation solvents. The
material contains phenolic functionality and provides a final resin system with very high thermal stability properties and Tg’s
in the 150 – 185 °C range,depending on the resins employed. As part of the curing agent system,the new flame retardant
becomes incorporated into the cross-linked matrix as part of the polymer network. The curing reaction behaves like a typical
novolac resin cure and no modifications in press cycle or B-stage conditions are required. This paper discusses the properties
of the new flame retardant material along with use data depicting the handling characteristics from the formulation
development stage to the final laminate. The laminates made using this flame retardant system meet UL-94 V-0 requirements
and pass the Pressure Cooker and T-260 tests.

Enclosed print heads have recently been available to circuit board manufacturers as an alternate technology to conventional
squeegee printing. By design,enclosed print heads offer several advantages one of which is isolating the solder paste from
the ambient environment thereby stabilizing the rheology of the paste for longer periods. In addition,enclosed print heads
decouple print speed from the pressure within the paste allowing for better control during the print operation.
Very little has been done to demonstrate the advantages of enclosed print heads with regards to print process capability. This
will be the topic of the paper presented here. The study compares the performance of two designs of enclosed print head to
that of a squeegee system on the basis of deposit consistency.

The printing process is always highlighted as contributing the most process defects to a surface mount manufacturing
production facility; typical values presented are around the 60% range. Fact or not it does focus the mind on the
component parts of a mass imaging process especially if it is “hidden” – such as Tooling.
The standard tooling solutions on offer are either fabricated tooling plates or manually located magnetic pins. Both of
these solutions have several drawbacks with regards to set-up time,expense and the inability to support on components.
It is the last issue mentioned which is becoming ever challenging,as substrates become smaller the real estate in which
tooling support can be applied reduces,compound today’s thinner substrates and a real yield risk emerges.
This paper is focused on a new breed of tooling which conforms around the substrate and underside components –
Compliant. To carry out this investigation 3 tooling solutions will be tested,this will include a metal plate to form the
benchmark test. The compliant tooling solutions will be based around modules of pins,which form around the substrates
underside. The first system employs hydraulics to provide compliancy throughout the print cycle. The other solution
utilises pneumatics,which locks the pins after each set-up to form a rigid system.
To investigate all tooling solutions fully a panellised test vehicle fabricated in 0.6mm,1mm and 1.6mm FR4 with pre
assembled SMT components and heavy routing will be utilised throughout.
An automatic laser optic system will be used to measure the solder paste volume,heights and area across the entire
substrate. This data will establish any variation of system to system and indicate which systems have the greatest
flexibility

The research discussed in this paper uses an innovative enhancement technique for printing High Density substrates. The
technique takes advantage of high frequency low amplitude vibrations applied to the stencil at the time of the stencil/substrate
separation. Similar work has been performed in a previous study for the bumping of wafers,1 however the range of pitches
and bump heights addressed in the present work is different. The pitches and bump heights of interest are of the order of 200
and 40 microns respectively. The study shows that enhanced printing produces taller bumps and more uniform bump heights
than can be achieved with conventional printing without vibrations. The study concludes that the vibratory enhanced printing
technology represents an economical and attractive alternative for the mass bumping of High Density substrates.