This document is intended to help manufacturers minimize the risk of failures from tin whiskers. It is the consensus of the
iNEMI User Group that pure tin electroplating presents a risk in high-reliability applications,and that there are cost-effective
alternatives available to minimize this risk. This paper presents recommendations for Lead Free finishes for a variety of
applications and reflects the best judgment of the iNEMI User Group members,based on their own experiences and the
available data. The group has defined methods and tests intended to minimize the risk of tin whiskers creating functional or
reliability problems in electronic products. These recommendations include a combination of known mitigation practices,
process controls and some level of testing. Recommendations have been organized to provide easy-to-follow guidance on the
various Lead Free finish options. There are tables addressing every finish and base material offered commercially and
provides user acceptance guidelines for the various combinations. Also included are finish recommendations for separable
connectors and for buss bars and heat sinks.

As the electronic industry shifts to lead-free manufacturing,Sn whisker remains a key reliability concern. Several whisker
mitigation strategies have been adopted by the component manufactures,but not without controversy and heated debate. In
this paper,we will describe an innovative whisker mitigation approach for leadframe application. This approach can be
viewed as a drop-in replacement for the SnPb surface finish and can be introduced without significantly modifying the
current leadframe plating line process. Our investigations demonstrated superior whisker resistance of utilizing “thin tin over
nickel” compared to other whisker mitigation strategies practiced in the industry.

PCB assemblies with numerous BGAs often go through multiple BGA reworks but there is not much data to suggest its effect
on the long term solder joint reliability of the BGAs. This study is focused in addressing this gap and to provide a
recommendation for the number of BGA reworks that could be performed without any impact to solder reliability.
To prepare a test unit for evaluating BGA solder joint reliability after multiple reworks,many BGAs are required for the
multiple detaching / attaching process. This traditional method is labor intensive and expensive. A novel method for test unit
preparation of multiply reworked BGA is explored here. In this method,instead of detaching an old and replacing a new
BGA,the same BGA unit was reflowed on the assembly multiple times to mimic the thermal excursion cycles. In the last
rework cycle,a new BGA replaces the old one that has been reflowed multiple times. The validity of the novel method was
explored by comparing the solder joint microstructures obtained by the traditional and novel methods. The interfacial
intermetallic layers,resulting from both the traditional and novel methods using identical temperature profiles and after up to
5 rework cycles,had comparable intermetallic thickness and porous microstructure. In the unit prepared with the novel
method,the intermetallic layer became thicker and denser as rework cycles progressed,but after the last rework cycle in
which a new BGA was added,the intermetallic layer became thinner and porous.
Using the novel method,two different BGA packages were chosen,9x15mm CSP and 45mm FCBGA,to study both small
and large package designs. Solder joint reliability was evaluated by performing Accelerated Thermal Cycling (ATC) and
mechanical shock testing on the as-assembled controls,3 and 5 reworked samples. Test results showed that there was no
impact to solder joint reliability due to multiple BGA reworks.

The use of the Area Array Package and in particular,Ball Grid Array (BGA) technology in the electronics industry continues
to increase due to the fact that this package type allows for a greater I/O count in a smaller area while maintaining a pitch that
allows for ease of manufacture. The original assembly process,and to a large extent the rework process for BGA devices
utilizing tin/lead solder materials,has proven to be fairly trouble-free. Environmental and legislative concerns are forcing
many manufacturing facilities to transition to Lead Free materials and processes that don’t have the same long history of use
as tin/lead products.
It is now common knowledge that Lead Free solder will exhibit reduced wetting when compared to traditional tin/lead
solders. As more and more assemblies are transitioned to Lead Free materials,it is important to understand what impact the
variables of solder wetting will have on the reliability of these Lead Free assemblies. What effects will a “flux only”
attachment of the BGA have on the wetting characteristics? What about paste print volume or the size and shape of the
stencil apertures?
This paper will review the results of thermal cycling of BGA samples that were processed with Lead Free materials utilizing
different solder paste print parameters,flux attachment only,and different BGA land pattern diameters. The goal will be to
use the resulting correlations to develop guidelines for the best reliability of reworked BGA devices.

The trend of increasing complication in the rework arena continues. Sources of today’s rework challenges include the
development of smaller and smaller components and the continued difficulty of reworking BGAs (with defective,deformed,
or missing balls). Add to that,the necessity for contract manufacturers to have a reliable solution to reduce waste continues.
The need exists to blend “typical” rework (SMD components,lead-free solder and 0201) with more complex rework,such as
single ball reballing. Or,simply put,to reuse BGA components that have failed capillarity tests or have arrived from the
manufacturer as defective parts.

Laminated woven glass reinforced polymer matrix composites (PMC) are commonly used in the electronics industry as a
robust and effective substrate for circuit boards. In such applications,reliability is extremely important. The laminated
composites must undergo several processing steps to introduce circuitry,during which interlaminar damage is sometimes
introduced,leading to blisters and delaminations. Therefore,it becomes important to understand the factors that control the
interlaminar shear strength (ILSS) of the laminate. In this study,the ILSS of a laminated PMC was examined as functions of
matrix phase additions,the matrix mixing procedure,the glass fiber finish chemistry and concentration,and the matrix
rheology. Matrix phase additions,mixing,and glass finish were found to significantly effect the ILSS,while the matrix
rheology had less of an impact.

The proposed revision of IPC 4101 - Specification for Base Materials for Rigid and Multilayer Printed Boards contains
new slash sheets describing FR-4 base materials compatible with lead-free assembly. These specification sheets also
outline requirements not found currently for FR-4 including Td,T260 and T288. In order to achieve minimum
performance criteria,toughening agents have been incorporated into the FR-4 resin systems both for 135 and 170°C
materials. Current modifiers for toughening thermosetting systems exhibit significant drawbacks including depression
of the glass transition temperature,instability of the formulation and difficulty of use. Core Shell Rubber (CSR)
particles have been used successfully for more than 40 years in thermoplastic applications but have had limited success
in thermosetting systems due to difficulty in dispersing the solid powder into the resin system.
We have developed a proprietary process for dispersing CSR domains into various thermosetting resins. The CSR
particles are perfectly dispersed and remain so during storage under a variety of conditions and after the formulating
process is complete. The resulting FR-4 composite exhibits improved inter-laminar adhesion,fracture toughness and
lap shear strength without depressing the glass transition temperature or other thermal properties related to the cross
link density. The CSR particles are supplied as a 25% concentrate in an epoxy resin chosen by the formulator such as
a liquid Bis-A or multifunctional brominated epoxy thus minimizing initial development work.
This paper will discuss the merits and use of these novel toughening agents for thermosetting systems for lead-free
compatible base materials.

New substrates for ultrathin multilayer boards consist of ultrathin glass fabric and a novel low elastic modulus thermosetting
resin system. They are composed of various lineups with the same resin system for the first time in the world; laminate
(TC-C-100),prepreg (TC-P-100),resin-coated copper (TC-F-100),adhesive resin film (TC-A-100). By using these lineups,
it is possible to fabricate a variety of thin multilayer PWB. In particular,with TC-C-100 and TC-F-100,you can easily
fabricate a bendable part and a multilayer part in a unity. Since the cover-layer and the bonding sheet are unnecessary,you
can make thinner PWB of higher density. In addition,they will make the circuit manufacturing process simpler to provide
thinner and bendable multilayer PWB with higher reliability.

Currently there is not a specification within the IPC for the DK and DF of E-Glass reinforcements and there is no
requirement to report the DK and DF of the glass formulation used to produce E-glass yarn. Without a specification,
performance of reinforced PWB substrates can be subject to significant variation depending on the supplier of the fiberglass
cloth. In an effort to understand the impact on the electrical performance of PWB substrate materials related to the choice of
fiberglass yarn manufacturer,FR4 laminates were produced using fiberglass cloth woven with yarns from specific vendors
and tested for their dielectric performance.

As an increasing amount of functionality is crammed into today's mobile phones,designers must find ways to save
board area. Two common solutions are the use of embedded passives and the use of smaller (0201) discretes. In
this paper,we examine the cost and area tradeoffs between small discretes and embedded polymer thick resistors.
Three typical mobile phone designs are analyzed using high volume assembly and state of the art board fabrication
techniques for scenarios with either small discretes or polymer thick film (PTF) resistors. The size and cost impacts
of each option are presented.