The enactment of the Restriction of Hazardous Substances (RoHS) Directive is prompting significant changes in solder paste
formulations and their process conditions as manufacturers move to Lead Free electronics assemblies. The residues
remaining after reflow of these new Lead Free materials are proving much more difficult to remove. This study evaluates the
cleaning capability of aqueous,semi-aqueous,solvent,and vapor degreasing including co-solvent products and processes.
Lead Free eutectic solder pastes from three leading suppliers were selected and cleaning results were evaluated and results
are compared to leaded eutectic materials.

As the electronics industry moves toward the implementation of Pb-free soldering,the impact on the assembly process must
be considered. One process that is often over looked is the cleaning of assembled printed circuit boards. How will the
introduction of lead free material impact the cleaning process?
A number of studies have proven the poorer wetting of SAC 305 alloys and many of the other Pb-free alloys as contrasted to
Sn/Pb during the soldering process. To address this issue,solder paste manufacturers researched and advanced flux
technologies to improve soldering yields. Many of the advanced flux technologies employ modern “exotic” compounds,
which often increase the difficulty of removing post-soldering residues. It is evident that both cleaning equipment and
cleaning chemistry must be modified to enable effective and consistent cleaning of Pb-free flux residues. It is also evident
that the best overall cleaning solutions will be provided by cleaning equipment and cleaning material companies working
together to optimize their products.
This paper discusses extensive cleanliness testing of over 70 Pb-free soldering materials. The data suggests increased
difficulty when cleaning Pb-free post-soldering residues. Based on the data,this paper discusses advances in cleaning
material and cleaning equipment mechanical designs that will optimize the cleaning of Pb-free flux residues. This paper will
detail the changes made in the cleaning equipment for optimizing the cleaning material advancements in industry standard
cleaning equipment.

Cleaning prior to conformal coating ensures optimal adhesion. In fact,a number of contaminations that are created during the
soldering steps significantly impair the cross linkage and can be safely removed by an adequate cleaning process. Specific
analytical methods are therefore highly recommended in addition to standardized cleanliness test procedures. This article sets
out to reflect on the latest study conducted,highlighting for example the characterization of encountered contamination for
eutectic and lead-free materials as well as their respective impact on quality and reliability. It is noteworthy to already point
out that the use of lead-free products will make cleaning,prior to conformal coating,an even higher necessity.
There has been a clear and consistent increase in the demand for no-clean (eutectic as well as lead-free) products over the last
few years. This trend coincides – and is likely correlated – to the growth of observed in-field service failures,particularly
with coated assemblies.

A new organophosphorus curing agent,Fyrol PMP,specially designed for electronic thermoset resins was recently
introduced to the market. This paper describes the chemical structure and physical properties of this material. This curing
agent has a unique mechanism of cross-linking epoxy resins. Because of high functionality it allows achieving high Tg and
good thermal properties required for lead-free soldering. About 20 to 30 wt. % this material completely cures epoxy resin
and provides a V-0 UL-94 flammability rating in the copper clad laminates. The loading of the material can be decreased to
10 wt. % when it is used in the combination with alumina trihydrate (ATH). In typical FR-4 laminate formulations,a glass
transition temperature (Tg) of 150°C or higher can be achieved . Co-addition of benzoxazine resin raises the Tg to 190°C. The
laminates pass the Delamination Test at the temperature of lead-free soldering (288°C) and securely pass the Pressure Cooker
Test.

Different legislations or draft directives target the restriction or the ban of the use of lead in the world. The law banning
lead-bearing electronic products (with a few exemptions) in the European Union (EU) will be implemented in July 2006.
China is considering adopting a similar law soon. In addition to the legislative pressure to reduce lead exposure,
marketing rewards also explains the trend to lead-free solder,although usually more expensive. Several Japanese
manufacturers have already commercialized products soldered with lead-free alloys. Finally technical requirements such
as higher in-use temperature in automotive applications tend to favor higher temperature melting point solders.
Consequently,it is expected that lead-free soldering will become the new standard in the future.
The change to higher temperature solder alloys will directly affect the reflow temperature profiles. In parallel,the
complexity of the boards is increasing,leading to thicker multilayer structures. Laminates will thus be submitted to
higher temperature for longer time through multiple reflow cycles. It is critical to understand how this translates into new
technical requirements for the laminates,especially thermal resistance. Results suggest that conventional FR-4 resins
might still be suitable for standard FR-4 applications that need only a few lead-free reflow cycles. When the number of
cycles increases,enhanced resin systems must be considered to avoid in-process failure. Highly thermo-resistant products
are suitable for complex multilayer build-up or for applications targeting high in-use temperature. In addition to thermal
stability,other key laminate parameters are electrical properties,adhesion,toughness and coefficient of thermal
expansion (CTE).
This paper also highlights new facets of the impact of lead-free soldering on the laminate requirements. The thermal
stability data of various epoxy systems are described and related to specific applications needs. We propose a complete
portfolio of epoxy systems available worldwide,from conventional FR-4 resins to highly thermo-resistant systems,
halogenated or halogen-free,with standard or enhanced dielectric constants. Some systems are very suitable for filler
loading,leading to low CTE laminates.

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.