Regulatory restrictions and environmental needs are moving the electronics industry towards lead-free solders and other
environmentally friendly materials. This massive effort has resulted in numerous efforts across the supply chain – this
involves qualifying materials and equipment,designing products and processes followed by exhaustive test procedures and
qualification.
This paper reflects some of the materials characterization efforts performed to accommodate the changes in assembly
processes. A look back at the life cycle of a PCB base laminate indicates that the substrate is exposed to numerous thermal
cycles at PCB fab houses and final board assemblers. This effort is focused on identifying and quantifying changes due to the
same.
It is crucial to characterize the effects of processing conditions on material properties to predict product performance; the
experimental plan involved evaluating changes in base material substrate properties as a function of multiple reflow cycles.
The following properties were evaluated – Glass Transition Temperature (Tg),T-288,Decomposition Temperature (Td),%
Expansion (50-260°C),Temperature of failure by TMA,and Dielectric Constant (DK).
Test vehicles were built with the same glass style and had the same construction. The reflow profile used was a typical “Lead
Free” cycle used for the qualification of substrates and PWB’s. The Lead Free profile used had substrate exposure time above
260C of 20 seconds,exposure above 220C for 110 seconds,with a peak temperature of 266C.
Each substrate material was exposed to 1 through 10 reflow cycles unless there was premature decomposition. Furthermore,
a range of base materials (Low – High Tg,Enhanced electrical,Filled substrates,different curing agents and resin
chemistries),were evaluated for this study. All laminate tested were 0.062 inches in thickness and clad with 17 micron thick
copper foil on both sides.

Rarely does a day pass by without a discussion centered on lead free manufacturing and it’s future impact on global
electronics assembly. The WEEE and RoHS directives drafted in January 2003 with a focus on electronic product recycling
and a ban of six hazardous substances in electronics products has created quite an industry buzz. European member states are
responsible for passing their own legislation making the directives law and binding in their respective countries. The WEEE
directive has slipped implementation in many countries as establishing recycling logistics appears to be more difficult than
first thought. On the other hand,RoHS compliance is moving along at a fast pace with many companies finding suitable
solutions and replacements for Sn/Pb solders. Engineers are now faced with optimizing the process variables around these
new material properties. Many recent studies have analyzed the effect / impact of Lead Free solder paste implementation on
a multitude of SMT processes including solder joint strength,wetability of SMD leads as well as pads on the PCB with a
variety of board finishes and solder paste compositions. Hardly a day goes by where you don’t see an announcement about a
new Lead Free implementation Workshop.
This study will focus on the stencil and squeegee blade and their impact on the Lead Free solder paste-printing process.
Three different stencils,three different Lead Free solder pastes,and five different squeegee blades are included in the study.
The Benchmarker II stencil test pattern was used as a tool in the evaluation. Of particular interest is the surface roughness /
smoothness of the stencil squeegee side surface. It is demonstrated that this surface has a dramatic influence on the minimum
squeegee pressure for metal squeegee blades to achieve clean wiping of the Lead Free solder paste from the stencil surface.
In addition to the surface finish of the stencil it was found that the type of Lead Free solder paste and the type of metal
squeegee blade used also played a roll in determining the minimum squeegee pressure to achieve clean wiping of the solder
paste.

Thermoplastics have started to gain acceptance in some of the more challenging areas of advanced packaging,including
MEMS,where lower cost,cavity style packages are required. Thermoplastics,like LCP,PPS and PEEK,can withstand
exposure to over 300oC thus assuring lead-free solder capability. Many polymers offer superior moisture resistance,can be
formed into micro-precision packages in just seconds,and are easily recycled. Epoxies,the non-hermetic package standard
for more than 50 years,can’t be remelted for reuse,have unremarkable moisture properties,and typically contain elements,
like bromine,that put them on the environmental target list. Some halogen compounds have already been banned.
Fortunately,several modern high-performance halogen-free thermoplastics are inherently flame retardant and these nontoxic
materials have an excellent record of use in telecommunications,medical,and automotive fields.
This paper will describe advances in thermoplastic packaging produced by injection molding (IM),including designs for
MEMS,MOEMS,power chips,high-intensity LEDS,and photonics. The processes include shaping,formation of
conductors,and enclosure by laser or dispensed adhesives for lid sealing. The newest concepts,such as the 3D stackable
package,will also be discussed in terms of thermoplastics.

As wireless products use higher frequencies and demand higher density packaging solutions,the roles of electrical
interconnects and substrate technologies become increasingly important. Flip chip technology has demonstrated significant
benefits especially through low interconnect losses. However,advances in wire bonding have also offered some
improvements,without the added cost for bumping,pad modification and redistribution. Using ribbon,instead of round wire,
for instance,has numerous benefits including reduced high frequency transmission loss and reduced risk of cratering (due to
reduced force requirement). The mechanical and electrical properties of ribbon bonds were investigated in this paper.
A systematic approach was developed for optimizing the key parameters of the bonding process. A three-variable
implementation of the response surface method was demonstrated to be a viable technique for optimizing the strength and
yield of the bonding process. The optimization process was then applied to bonding on organic RF substrates allowing a
comparison of the impacts from dielectric materials,metalization thicknesses,wire length and wire shape to yield and
strength. Finally,the electrical performance of various wires and substrates was compared using S-parameter measurements
from 5 to 35 GHz. The results of 1x10 mil,0.5x2 mil ribbon and 1 mil round wire were then compared,illustrating the
opportunity for improvements to transmission loss.

One manufacturing process used to attach RFI shields for medical applications/cellular phone circuit board assemblies
consists of “snapping” the shell-like shields onto solder spheres that are soldered to printed circuit board [PCB] pads [1]. The
snapped on RFI shields do not require soldering onto the printed circuit board and can be removed if necessary. In order to
create a large enough solder balls for the shell to snap onto,a large quantity of material must be available.
Currently this process is a two-step process. The first process step requires solder paste to be printed onto the printed circuit
board pads using standard solder paste printing process. The second step is to print or place solder spheres onto the printed
solder paste deposits. The printed circuit board with solder paste and solder spheres are then reflowed to achieve a ball height
sufficient for the RFI shield to snap onto. This two-step process requires either the use of a component placement machine
(pick and place) or the use of specially designed print head that is available on only limited printing equipment. The goal of
this experimentation is to develop a process that can achieve the ball height requirement using only standard solder paste
printing technique and virtually any solder paste printing equipment.
Recently,work has been completed to identify a stencil design and solder paste formulation that will allow sufficient solder
paste to be printed and form a large solder sphere after reflow to permit RFI shield attachment. This ‘SnapShot’ shield attach
process eliminates the requirement to purchase solder balls and the additional equipments need to place or print the solder
balls. This paper will present the results from formal studies that have been completed to verify the performance of the solder
paste printing process for the ‘SnapShot’ shield attach process.

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.