The Massachusetts Toxics Use Reduction Institute (TURI) has sponsored a consortium of Massachusetts based
corporations to investigate lead-free (Pb-free) surface mount soldering technology. The current effort is a Design of
Experiments (DOE) analysis using three NEMI recommended tin silver copper (SnAgCu) alloys from three different
solder manufacturers,five Pb-free PWB surface finishes,and two reflow environments. The consortium designed a
special test PWB and that was used in the experiments. A modified visual test procedure was developed and the
results are presented based on statistical analysis. Test PWBs with BGAs,leaded and chip components will be
subjected to thermal cycling,and then tested for mechanical degradation. Standard tin-lead (SnPb) eutectic solder
63/37 reflow samples were used as a control.
Components on these test substrates include plastic and ceramic leaded SOICs,FPQFPs,an LCC,45mm square ball
grid arrays (BGAs) and small passive devices. This paper will discuss results along with the issues associated with
each lead and PWB finish. Conclusions from this paper can be used as a guide to future product offerings,and to
proper testing,reporting methods and recommendations to satisfy future Pb-free requirements.

Intermetallic formation and growth were studied for the alloys Sn-3.2Ag-0.8Cu,Sn-3.5Ag,Sn-0.7Cu,and Sn-9Zn.
Coupons of solder joints (prepared by melting some of each solder alloy on a copper-plated circuit board) were
subjected to thermal aging tests for 20,100,200,and 500 hours at 70,100,and 150oC. Also,the activation energies
for the formation of each intermetallic compound and the total intermetallic layer for the four copper-solder systems
were determined. The results confirm that the formation of intermetallic layers is controlled by diffusion and that the
intermetallic layers grow by thermal activation in a parabolic manner. The total thickness of the intermetallic
compounds produced at 150oC for 500 hours and the activation energies for the total intermetallic layer in the four
copper-solder systems were: 14 µm and 0.74 eV/atom for Cu/Sn-3.2Ag-0.8Cu,13 µm and 0.85 eV/atom for Cu/Sn-
3.5Ag,14 µm and 0.68 eV/atom for Cu/Sn-0.7Cu,and 19 µm and 0.35 eV/atom for Cu/Sn-9Zn.

The introduction of Pb-free solder into the electronics industry has required changes to the standard surface mount process.
The largest changes are in the reflow process,as Pb-free pastes require higher temperatures and tighter process controls than
standard SnPb solders. The goal of this work was to develop a reliable Pb-free process utilizing SnAgCu solder paste as a
replacement for SnPb solder paste. In general,SnAgCu solder pastes recommend a peak temperature of between 242°C to
262°C as compared to the 208°C to 235°C commonly utilized for SnPb solder. Due to the higher reflow peak temperature;
the use of some components may not be feasible for Pb-free assembly. A large number of commonly used components are
sensitive to the standard higher peak temperatures of 235-240°C. One of the major goals of the work was to see if new
profiling technologies could be used to reduce changeover time from existing SnPb solder profiles to Pb-free profiles. This
was done over a variety of test boards ranging from a cell phone emulator to a board with a flexible interposer mounted on an
aluminum backing. The second major goal of the study was to determine the lowest possible peak temperature required for a
reliable Pb-free process. During the course of the work,yield results were recorded for various peak temperatures and SEM
analysis was done to look at the intermetallic growth and grain structure of the solder joints processed at the various peak
temperatures.

Within the Surface Mount Assembly (S.M.A.) process,solder paste is primarily used as a mechanical and electrical
connection. Solder paste is generally deposited using a mass imaging process,such as squeegees,however this paper
will utilize the enclosed print head technology. The process associated with mass imaging is a critical and
demanding stage in the soldering phase of S.M.A. It has been documented many times that this process contributes
more than 60% of all S.M.A faults; This being the case it illustrates the requirement to have a full comprehension of
the mass imaging process.
With legal and commercial pressure put on to remove lead from within the electronics sector,the solder paste alloy
is obviously under review. Much work is being carried out on the metallurgical properties of these lead free solder
pastes such as joint strength and compatibility within the manufacturing process. However,this paper will focus on
investigating the process window for mass imaging of lead-free materials. The major influences within the mass
imaging process have been documented in numerous studies using lead rich materials. However,the material used to
replace the Pb component changes the solder paste properties and therefore the characteristics of the print medium.
Therefore to conduct this study a two level three factor Design of Experiments with center points will be utilized.
The factors investigated in this paper will be print speed,paste pressure and separation speed. Three material
suppliers will be used to ensure the results give a broad representation of the significant effects on the process
window. Comparison to a lead rich material will also be carried out to allow an evaluation to be concluded. Each
paste will be tested for paste release transfer efficiency using the optimum setting concluded from the
characterization stage.

The popular tin (Sn) rich lead free solders are causing severe corrosion to many of the materials used in today’s
Wave Solder systems. Users are experiencing higher maintenance frequency and reduced life of wave solder
machine components. This paper describes the effects of Sn rich solders in contact with various materials and
discusses alternate methods to alleviate this problem.
In cooperation with the Metallurgy Department of the University of Missouri - Rolla,the Sn corrosion effects were
studied for stainless steels,coated stainless steels,titanium,cast iron,and other materials. Corrosion effects and test
results are presented for each of these materials. Optical and scanning electron microscopy and x-ray emission
chemical analysis were the primary tools used in the evaluation of failed samples. Based upon this research and field
trials,recommendations are given which address the expected field life,economic impacts,and materials selections
for new or used Wave Solder equipment.

Wave Soldering continues to be a necessity for many applications in the PCB assembly arena. One of the drawbacks
to the Wave Soldering process is the high cost associated with maintaining and operating the machines. Dross
production and removal is one of,if not the highest,cost associated with operating a Wave Soldering machine.
Safety,environmental,productivity and material cost concerns have made dross handling an undesirable activity.
This paper examines the available dross management technologies and reviews a promising new technology
available for recycling dross within a Wave Soldering machine. With this new technology,cost savings are
significant with investment payback in months versus years. Metallurgical analyses,field data,and cost analyses are
given for various means of handling and recovering solder from dross.

The electronic industry is under extreme pressure to remove tin-lead solders from electronic components. Pure tin is
one of the alternatives and may be the simplest system as a “drop-in” replacement for SnPb surface finishes.
However,fear of “whiskers” has been a major concern inhibiting its imple mentation. This is because that tin
whiskers,with a length from a few micrometers to several millimeters,may grow from electroplated Sn and cause
electric shorts in electronic devices,particularly in fine-pitch high I/O (input/output) components.
In APEX2002,we described our systematic and in-depth investigation of various factors affecting whisker growth,
and the driving force for whisker formation. In this paper,we will discuss various methods for minimizing or
eliminating whisker growth,which are based on our current understanding of the whisker growth mechanisms.

Tin alloys such as Sn 0.7% Cu and Sn 2%Bi were identified as a viable alternative to tin-lead finish. Electroplating
of these alloys is challenging because of great difference in reduction potentials of the individual elements and
usually associated with strong immersion deposition and poor alloy control. To overcome these problems we
utilized metal specific non-complexing organic additives,which can significantly slow down or completely inhibit
deposition of the alloying element in certain range of potentials. In this paper,we present the recent developments
for Sn-Bi and Sn-Cu plating chemistries. We also discuss materials properties of the deposits and different plating
applications.

This paper provides an assembly process comparison of Pb-free alloys with a Sn/Pb alloy using a test vehicle
designed to resemble real world manufacturing applications. Four different Pb-free alloy systems,including two
compositions in the Sn/Ag/Cu alloy system,are investigated,and their board level assembly processing
characteristics are compared to the eutectic Sn/Pb alloy for a variety of surface mount components and packages,
and through-hole components. Presumably,Pb-free technology will adopt the same family of components,with
alterations only in their package materials. The key advantage of this approach is that the focus is on evaluating the
Pb-free manufacturing process and verifying its capability,independent of a specific component. As a result,a
matrix of different families of components,such as chip components,peripherally leaded components,ball grid
array packages,and chip scale packages with varied pitch sizes has been incorporated. The components were
assembled on printed circuit boards having five different Pb-free surface finishes. The sequential approach has been
adopted that involves the design of the test vehicle and component selection,comparison of printing characteristics
for Pb-free pastes,and comparison of processing defects. This paper is a follow-up to one that appears in the
proceedings of the 2003 Pan Pacific Microelectronics Conference. The earlier paper discussed in detail the design of
the test vehicle,stencil design and comparison of printing characteristics for Pb-free pastes. This paper discusses the
comparison of processing defects. The results of the assembly process defects are based on visual and x-ray
inspection of the assembled boards. Finally,a performance index is calculated to provide a relative comparison of
different combinations of Pb-free alloys and alternative surface finishes.

Shelf life is one of the most important characteristics of solder paste. Many pastes exhibit good print characteristics
when fresh but then suffer rapid degradation. Although rosin based pastes are most susceptible to this phenomena
water-soluble solder pastes can also see degradation in rheological properties.
In order to determine what parameters are most important for the stability of water-soluble paste an extensive study
of the change in rheology with time was undertaken for a series of water-soluble pastes. The parameters investigated
included alloy type,carrier base composition,surfactant properties,and solvent carrier composition.
Results indicate that the decay of the rheological properties is strongly influenced by alloy type and can be,to some
extent,retarded by proper choice of the activator package.