As we progress in the 21st century,electronics manufacturing will need more and more precision. Parts will get more complex since more components have to be assembled in smaller spaces. Circuit boards and other electronic assemblies will become more densely populated; spacings between components will be shorter. This will require precision manufacturing and efficient cleaning during and post manufacturing. In addition,with population and technology progressing,larger amount of greenhouse gases will be emitted resulting in higher global warming. Intense research effort is going on to develop new generation of chemicals to address both cleaning and global warming issues. Low global warming solutions in refrigeration and as insulating agents are already in the marketplace. This paper will detail the development of a new very low global warming potential environmentally friendly non-flammable solvent with excellent cleaning abilities. Environmental properties,cleaning efficacies,stability in various conditions,and compatibility with plastics,elastomers,and metals of the solvent will also be described in this paper.

For many years there has been a huge disconnect between the engineers that design the assembly and the chemists responsible for developing the assembly materials. In short,engineers and chemists don’t speak the same language.
•In today’s HDI environment,this disconnect in language can cause more issues than it solves. The challenges of cleaning the smaller pitched components used in the HDI World means that the two disciplines need to be married together to better understand how to overcome these challenge.

Boundary-scan (1149.1) technology was originally developed to provide a far easier method to perform digital DC testing to detect intra-IC interconnect assembly faults,such as solder shorts and opens. Today’s advanced IC technology now includes high-speed differential interfaces that include AC or DC coupling components loaded on the printed circuit assembly. Simple stuck-at-high/low test methods are not sufficient to detect all assembly fault conditions,which includes shorts,opens and missing components. Improved diagnostics requires detailed circuit analysis,predictive assembly fault simulation and more complex testing to isolate and accurately detect all possible assembly faults.
Several cases will be presented to illustrate how usage of circuit information and predictive analysis of potential assembly faults will provide more precise and accurate diagnostic information. Special attention will be paid to the increasing usage of high-speed differential logic interfaces and their associated discrete components and connectors,which increasingly have no probing access and then traditional incircuit test cannot be accomplished.
The material will also include a discussion of future challenges and their potential impact on diagnosis of assembly faults. Many in the industry are very much aware of the decline in probing access and are wisely skeptical of claims that providing a function test will provide an accurate and useful diagnostic indication upon failure. This material is intended to further the development and evaluation of solutions that not only detect,but usefully diagnose assembly faults….which clearly are not disappearing any time soon!

1. What is BIST
2. What is DSL
3. DSL test items
4. Digital & Analog DSL test
5. BIST on DSL
6. Comparison & Benefits

In an effort to reduce volatile organic compound (VOC) emissions within our environment,policymakers
have encouraged and/or mandated that electronics manufacturers change from alcohol-based VOCcontaining
fluxes to water-based VOC-free flux alternatives. As a result,the use of VOC-free fluxes is
growing throughout North America,Asia and Europe.
The purpose of this study is to explain several factors relating to the use of a VOC-free flux in the soldering
process and their impact on testing and product reliability. These factors include; the effect of varying types
of acids used in flux formulations and their impact on Ion Chromatography (IC) and Surface Insulation
Resistivity (SIR) test results and weak organic acids (WOA) solubility and their influence on the electrical
integrity of assemblies. This paper shall provide valuable insight into the outcome of acid-solvent
interactions.
The transition to VOC-free fluxes from alcohol-based fluxes can be a challenge and may require several
changes in the assembly process. Compounding these challenges is the increased use of lead-free alloys
with the looming expiration of the RoHS exemptions. Additional pressure has been placed on solder flux
manufacturers to meet the newer,more restrictive ionic test requirements and updated SIR test criteria.
AIM Product Development Group’s study consisted of using several organic acids,each individually
incorporated into both a generic VOC-free and a generic alcohol flux base. Half the test boards were sent
out for IC testing per IPC-TM-650 2.3.28 to determine the level of WOA. The other half were sent for SIR
testing per IPC 2.6.3.7. The fluxes were also run on a wetting balance to determine solderability
differences. The test results of the alcohol-based fluxes were not included in this study.
Additional important considerations related to VOC-free fluxes addressed in this paper include wetting
characteristics,organic solvent characteristics,the importance of a flux’s collapsing foam head,issues
related to corrosivity,shelf life,manufacturability,handling and storage. All of the aforementioned issues
were taken into consideration when developing the flux base for this study.

No-clean soldering processes dominate the commercial electronics manufacturing world. With the explosion of growth in handheld electronics devices,manufacturers have been forced to look for ways to reinforce their assemblies against the inevitable bumps and drops that their products experience in the field. One method of reinforcement has been the utilization of underfills to “glue” certain surface mount devices (SMDs) to the PCB. This provides additional mechanical strength over and above the soldered connections. Bumped SMDs attached to the PCB with a no-clean soldering process offer the unavoidable scenario of the underfill coming in contact with a flux residue. This may or may not create a reliability issue. No-clean solder paste flux chemistries can vary. Some have halogens and others do not. Some have standard residues and others have residues optimized for pin probing. There are also a number of underfill chemistries on the market. Furthermore,underfill curing conditions vary depending on whether the SMDs are exposed on the surface of the PCB or underneath an RF shield. This paper will discuss an experiment designed to measure the electrical reliability of various combinations of underfill and no-clean flux residues,as measured with J-STD-004B SIR (IPC-TM-650 2.6.3.7).

While it has long been known that the Cu6Sn5 intermetallic that plays a critical role in the reliability of solder joints made with tin-containing alloys on copper substrates exists in two different crystal forms over the temperature range to which electronics circuitry is exposed during assembly and service,it has only recently been recognized that the change from one form to the other has implications for solder joint reliability. Under equilibrium conditions the change from the hexagonal to monoclinic form occurs in the cooling solder joint at 186°C. However,cooling rates after common commercial soldering processes are typically faster than the rate that would permit complete transformation under such equilibrium conditions. In this paper the authors report a study of the effect of cooling rates on Cu6Sn5 crystals. Cooling rates from 200°C ranged from 10°C/minute to 100°C/minute and the effect of isothermal ageing at intermediate temperatures was also studied. The extent of the phase transformation after each regime was determined using synchrotron X-ray diffraction. The findings have important implications for the manufacture of solder joints and their in-service performance.

In this paper,we report on a comprehensive study regarding the morphology evolution and voiding of SnAgCu solder joints
on the central pad of two different packages – QFN and an Agilent package called TOPS – on PCBs with a Ni/Au surface
finish. Samples were isothermally aged at the equivalent of 0,2,7 and 14 years service life. Representative solder joints
were cross-sectioned and analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy
(EDX) in order to investigate the evolution of the solder joint morphology as a function of Au content and isothermal aging.
IMC thickness was measured. The effect of Au content on the void percentage was studied as well. The results show that if
copper is available to dissolve into the solder joint,the AuSn4 IMC from the bulk does not migrate to the interface as a result
of thermal aging. The IMC thickness grew with aging as expected,however with Cu base metallization the IMC was
dominated by Cu6Sn5,and with Ni base metallization on both sides of the joint the IMC was dominated by AuSn4. Voiding
analysis showed that thick Au metallization on thermal pads leads to more voiding and larger standoff height.

The continuous progression toward portable,high frequency microelectronic systems has placed high demands on material
performance,notably low dielectric constants (Dk),low loss tangent (Df),low moisture uptake,and good thermal stability.
Epoxy resins are the workhorses of the electronic industry. Significant performance enhancements have been obtained
through the use of PPE telechelic macromonomers with epoxy resins. However,there is a ceiling on the performance
obtainable from epoxy-based resins. Therefore,non-epoxy based dielectric materials are used to fulfill the need for higher
performance. The focus of this paper is on vinyl monomers such as triallyl isocyanurate (TAIC) and t-butyl styrene/divinyl
benzene (TBS/DVB) and their use with vinyl modified PPE macromers. When TAIC and TBS/DVB are cured by
themselves,the resultant material was extremely brittle. However,the use in combination with vinyl modified PPE
macromers,resulted in dielectric materials that exhibited major increases in toughness,very low dielectric properties,high
glass transition temperatures (Tg),and very low moisture absorption. Printed wiring boards made from a combination of vinyl
monomers and the PPE engineering macromonomer exhibited significant performance advantages over epoxy and modifiedepoxy
materials.

Over the past few years a new family of laminate systems has been developed to face the increasing physical demands of
withstanding Pb-free soldering processes used in the assembly of RoHS compliant products. Many of the materials have been
found to perform satisfactorily for consumer type products where reflow temperatures peak around 245°C. However the high
end PWB designs for the telecommunicat ions and IT equipments typically tend to be more complex,thicker and therefore
have a much higher thermal mass than consumer products. In order to apply sufficient heat to enable satisfactory solder
reflow of surface mounted devices,the temperature of the printed wiring board can peak at up to 260°C. Add to that the
complexity of the board (typically double side assembled) and the requirement to be able to repair boards,then it is highly
possible that boards throughout their manufacturing cycle could see up to 5 thermal excursions up to this 260°C level
withstanding 20~30 seconds over 255°C. The ability of laminate systems to withstand the combined thermal exposure without
degradation or delamination and at the same time exhibiting consistent electrical properties is essential.
To meet the demand,a novel thermoplastic resin modified multifunctional epoxy system material has been developed. Silica
fillers have been carefully selected for ensuring the lower CTE. The material shows an outstanding heat resistance,reliabili ty
and toughness performance with complex BGA design (Pitch 0.8mm,through hole d iameter 0.25mm) on thicker (Thickness:
4mm PTH board and 3.2mm HDI board) PWB board comparing with currently available Pb -Free compatible materials. The
dielectric properties and other properties of this material will be presented.