With the predominance of no-clean soldering processes and ever decreasing component standoff,the industry has had to consider the reliability of,what may be,partially activated or “gooey” flux residues under component bodies. Similarly,questions have also risen about the reliability of flux residues resulting from the reflow of no-clean solder pastes that are “entrapped” under RF shields or “cans”,where escape of the volatile ingredients of the flux is greatly hindered. In this paper,discussion will be made regarding an experiment designed to mimic the aforementioned conditions and how these conditions affected the SIR performance of the no-clean flux residues. A variety of no-clean solder paste flux residues will be discussed,including a halogen-containing,Pb-free solder paste flux; a halogen-free,Pb-free solder paste flux; a halogen-free,Pb-free solder paste flux with a residue optimized for pin probing; and a halogen free SnPb solder paste flux.

Convection soldering remains the most common reflow process in electronic assembly,mostly in air,but sometimes using a nitrogen atmosphere to reduce oxidation.
On the other hand,vapor phase soldering remains a niche market: it has been dedicated for years for use on complex boards with heavy mass and/or a large mix of component sizes. Despite its excellent heat transfer capabilities and high wetting performance,this process suffered from weaknesses that prevented it from being used on a large scale: high fluid consumption (CFCs),high tombstoning effect,long process time,and the inability to integrate it into a production line.
In the last few years,vapor phase reflow technology has been improved: New fluids,with boiling temperatures up to 240°C,have been developed,the consumptions have been greatly reduced and the control of preheat and peak ramp rate has been improved,lowering the tombstoning effect.
With lead-free implementation,some limitations are observed on complex boards with convection ovens: the thermal reflow process window is reduced due to the higher temperatures required for SAC alloys,the maximum temperature allowed for fragile components,and the wide range of component sizes.
Vapor phase reflow might be an option to consider.
However,because of the relatively low peak temperatures and the elimination of oxidation with this process,a question may arise about the reliability of the paste residue. More unburned activators might remain on the board,which could cause some corrosion to develop,even when using no-clean solder pastes.
The purpose of this paper is to assess the reliability of several lead-free,no-clean paste residues after vapor phase reflow in comparison to convection reflow. We will use Surface Insulation Resistance (SIR) and Electrochemical Migration (ECM) according to IPC standards,in addition to the Bono test which has been proven to better differentiate the nature of solder pastes residues.

Electroplated Ni/Au over Cu is a popular metallization for PCB finish as well as for component leads,especially wire-bondable high frequency packages,where the gold thickness requirement for wire bonding is high. The general understanding is that less than 3 wt% of Au is acceptable in SnPb solder joints. However,little is known about the effect of Au content on the reliability of SnAgCu solder joints. The purpose of this study is to determine the acceptable level of Au in SAC305 solder joints. Three different package platforms with different Au thicknesses were assembled on boards with two different Au thicknesses using a standard surface mount assembly line in a realistic production environment. The assembled boards were divided into three groups: as-built,isothermally aged at 125°C for 30 days,and isothermally aged at 125°C for 56 days. All boards were then subjected to accelerated mechanical reliability tests including random vibration and drop testing. The results show that solder joints with over 10 wt% Au are unacceptable. If Cu is available to dissolve in the solder joint,then an Au content under 5 wt% will not significantly degrade the reliability of the solder joint. When Ni layers are present on both the board and component sides of the interface,this limits the ability of Cu to dissolve into the solder joint and hence an Au content under 3 wt% is acceptable. The failure mechanism for solder joints with high Au content is fractures through the AuSn4 IMC. Our comprehensive long-term reliability study did not confirm the finding by Ho et al. (2002) that the weak interface between (Au,Ni)Sn4 and Ni3Sn4 results in brittle interfacial failure. Additional findings confirmed the danger of placing parts near high stress areas and that a high level of voiding reduced reliability.

Spontaneously forming tin whiskers,which emerge unpredictably from pure tin surfaces,have regained prevalence as a topic within the electronics research community. This has resulted from the ROHS-driven conversion to “lead-free” solderable finish processes. Intrinsic stresses (and/or gradients) in plated films are considered to be a primary driving force behind the growth of tin whiskers. This paper compares the formation of tin whiskers on nanocrystalline and conventional polycrystalline copper deposits. Nanocrystalline copper under-metal deposits were investigated,in terms of their ability to mitigate whisker formation,because of their fine grain size and reduced film stress. Pure tin films were deposited using matte and bright electroplating,electroless plating,and electron beam evaporation. The samples were then subjected to thermal cycling conditions in order to expedite whisker growth. The resultant surface morphologies and whisker formations were evaluated.

Over the last few years,there has been an increase in the Evaluation and use of halogen-free soldering materials. In addition,
there has been increased scrutiny into the level of halogens and refinement of the definition and testing of halogen-free
soldering materials. The challenge has been that there has been no common standard across the industry in terms of halogenfree
definitions and the corresponding test methods to determine these. This has created confusion in the industry as to what
end users want and what soldering materials suppliers can actually provide. This paper will review the status of both halogenfree
and halide-free in terms of definitions,test methods and the limitations and accuracy of test methods used to determine if
a soldering material is halogen/halide-free or not. For halogen-free and halide-free definitions,the paper will review the different industry standards which are currently available and those being drafted,and it will discuss any similarities and differences. It will also cover the origins of some of the definitions mentioned in the standards. The paper will include a review of the accuracy and limitations of several test methods and preparation techniques for halogen and halide determination.

As interest continues in the development of non-halogen flame retardants for printed circuit boards,the requirements for robust thermal stability and lead-free solder compatibility also continue. With respect to developing “greener” electronic materials,one option available to the formulator is to use compounds that are reactive so they will become part of the cross-linked laminate matrix when cured. A well-understood example for doing this is to develop laminate formulations for epoxy resin systems that incorporate the flame retardant tetrabromobisphenol A,since it is completely reacted into the system. The advantages of using a reactive system can also be achieved with certain non-halogen flame retardants,such as the curing agent discussed in this paper. These types of reactive systems also become part of the cross-linked laminate matrix. This new flame retardant material was developed as a reactive phosphorus-containing flame-retardant curing agent with very high thermal and hydrolytic stability. It is intended for use in conjunction with epoxy resin formulations in use today. This paper describes the development of this flame retardant and the performance in laminates with comparison to some existing non-halogen systems.

This paper reports on further developments for an innovative copper deposition technology that was presented two years ago at this conference. At that time,the innovative technology was described as a way to replace conventional sputtering and vacuum deposition techniques while achieving greater feature diversity,lower cost,and higher performance. The advancements reported here include the extension of the technology to deposit thin (depths of 0.1 to 10.0 microns) copper with good adhesion on the interior of via walls that have been pre-formed in the base material. This process extension has been demonstrated on vias as small as 25 microns in diameter and on thin (7.5 to 12.5 micron) polyimide base materials.

Metal plating of epoxy polymer has been widely applied for industrial products for a long time,especially in the field of Printed Circuit Boards (PCB’s). This technique is one of the most important technologies of electronics devices with high reliability and guaranteed quality. The authors are developing a new concept of PCB’s for next decade generations to improved the techniques of which including more fine line circuitries,higher densities and narrower spaced conductor lines. An essential part of subject for this technology is to improve the weak copper adhesion peel strength on epoxy insulation materials. To obtain the good adhesion property of copper plating,it is now widely used the Pd Colloid Solution method. In order to further improve more excellent adhesion for next decade generation PCB’s,we are investigating Super Critical Fluid (SCF) method. In this paper,an attempt has been made to impregnate some metal complexes into epoxy resin and then decomposed the complexes to produce free metal in the resin by reduction . Using the deposited metal is efficient electro-less Cu plating can be achieved. We will discuss the selection of the metal complexes and impregnation conditions on the complexes as well as peel strength of the plating.

Base on our experience,HiP defect comes in various shapes and
forms. Some of the HiP looks like an ordinary open joint,while others have an eclipse profile. The tough ones to detect are those that look like an absolutely good solder joint.
Although the HiP detection rate on the 5DX AXI averages about 70%,this system is currently by far the most efficient tool in the industry to screen for such defects. After the flagged joints are verified at the 5DX repair station,the remaining marginal or questionable joints are sent to a high resolution manual 2D x-ray machine for failure analysis.

-BA flux: Water soluble BA flux has a higher HiP risk relative to NC BA flux,likely due to higher surface oxidation risks.
-Deflux: Washing process using water or DIW in combination with other solutions
may make HiP risk higher when compared to leaving flux residue as received*.
-SMT paste: HIP improved models have higher performance than standard LF paste.