Foresite has investigated many whisker failures and found that consistent high levels of chloride,sulfate and amines are present in and around the areas of whisker formation even in hot dry environments with high stress conditions in the solder joints.

Inkjet printing is of great interest in the field of electronics manufacture because its digital nature negates the need for
physical tooling. A wide variety of active and passive materials are currently being investigated for use in inkjet printed electronics. These include semiconductors,light emitters and photovoltaic materials as well as dielectric materials and straight forward conductors. The range of conducting materials that can be printed is somewhat limited by the constraints of inkjet printing. Ideally,particle sizes should be below 1 micron and the viscosities and surface tensions of the fluids need to be tailored to the particular printhead being used. Regardless of these limitations,various technologies are now being implemented in the production of circuit boards,interconnects and antennas by inkjet printing. The properties of these inkjet printed circuits do not currently mimic traditional PCB materials – in particular,the sheet resistances of inkjet printed materials tend to be significantly higher than traditional copper clad laminate and the minimum feature sizes are somewhat larger than state of the art semi-additive plating. However,inkjet printed circuit technologies are a still finding many
applications which are particularly well suited to their properties and the digital nature of their application.

The cracking and delamination of printed circuit boards (PCB) during exposure to elevated thermal exposure,such as reflow and rework,have always been a concern for the electronics industry. However,with the increasing spread of Pb-free assembly into industries with lower volume and higher complexity,the occurrence of these events is increasing in frequency. Several telecom and enterprise original equipment manufacturers (OEMs) have reported that the robustness of their PCBs is their number one concern during the transition from SnPb to Pb-free product. Cracking and delamination within PCBs can be cohesive or adhesive in nature and can occur within the weave,along the weave,or at the copper/epoxy interface (see Figure 1). The particular role of moisture absorption and other PCB material properties,such as out of plane expansion on this phenomenon is still being debated.

In recent years there has been an increasing emphasis on miniaturization of Board Mount Power (BMP) modules and electronic subassemblies. In addition there has been a shift from predominately through hole to predominately surface mountable modules using FR4 substrates. This trend coupled with the recent transition to Pb-free products has led to questions regarding Moisture Sensitivity Level (MSL) ratings of Power Modules and subassemblies. Attempts to apply J-STD-020 ratings to subassemblies may not be appropriate and has major implications on the packaging and handling of these products. In addition,there continue to be questions and concerns from manufacturers of power products related to MSL ratings of bare PCBs. Failure to properly protect PCBs from moisture induced damage during the fabrication of PCBs and PCB assemblies can lead to costly yield and reliability problems.
IPC-9592 was released in the Fall of 2008. It addresses Quality and Reliability issues related to Power Products. This document highlights the concern with potential reliability risks due to moisture sensitivity of BMP assemblies. Since there are no established industry standards to address this concern,it is left up to the manufacturer and supplier to take appropriate precautions. The PCB is one of the most moisture sensitive components in BMP assemblies. Vulnerability to delamination especially during Pb-free reflow soldering will be one of the main driving forces in determining BMP module MSL ratings. This paper will present results of moisture studies performed on Lineage Power PCBs and Modules. It will also suggest methods that will reduce the vulnerability of the PCB and the PCB assemblies to moisture induced damage.

The high temperature exposures associated with lead-free soldering of printed circuit boards (PCBs) can alter the laminate
material properties thereby creating a shift in the performance and reliability of the PCB and entire electronic assembly. The
knowledge of PCB laminate material properties and their dependence on the material constituents,combined with their
possible variations due to lead-free soldering exposures,is an essential input in the selection of laminates for appropriate
applications.
An experimental study is conducted on fourteen types of commercially available PCB laminate materials to assess the effects
of lead-free soldering process on key thermomechanical and physical properties. The laminates are classified on the basis of
their glass transition temperature (high,mid and low),type of curing agents (dicyandiamide (DICY) and phenolic),type of flame retardants (halogenated and halogen-free),and presence or absence of fillers. Laminate material properties [glass transition temperature (Tg),coefficient of thermal expansion (CTE),decomposition temperature (Td),time-to-delamination (T-260),and water absorption] are measured as per the appropriate IPC-TM-650 test methods before and after subjecting to multiple lead-free soldering cycles (namely,three reflow cycles,six reflow cycles,and a combination of one wave and two reflow cycles).
The lead-free soldering exposures resulted in variations in the material properties of certain FR-4 laminate material types. The extent of variations in the thermomechanical and physical properties under investigation are discussed as a function of
material constituents. It was found that the type of curing agent has a more pronounced effect on the response of materials to
exposures than the type of flame retardant or presence of fillers. For example,a significant variation in the Tg and CTE of certain DICY-cured materials is observed after the exposures. Also,time-to-delamination of DICY-cured materials decreased whereas phenolic-cured materials could retain their thermal stability even after exposures. An increase in water absorption after the exposures is observed in most of the materials. The exposures did not affect the laminate materials to an extent of changing their decomposition temperatures.

Lead-free selective soldering can result in extended times at high temperatures,which in turn can result in excessive dissolution of exposed copper,such as plated through holes. This phenomenon is more severe with lead-free,since the alloys have higher melting points,hence requiring longer times for the PTH to reach the higher temperatures,and the alloys typically have a greater capacity to dissolve copper.
This paper discusses a test method that characterises the dissolution rate of copper from PWBs. A PWB design was created
that allowed the time for the dissolution of a copper pad to be measured. With this quantitative method a soldering process
or an alloy can be characterised in terms of dissolution rates at specific conditions of temperature and flow rate. This methodology provided repeatable measurements that allowed the various experimental parameters to be isolated. Particular attention was paid at the flow rate of the molten solder. In fact,different alloys at the same temperature can have considerably different flow rates,due to the different viscosity at that temperature. The performances of seven lead-free alloys and a typical 60/40 Sn-Pb alloy were compared at three temperatures.
NPL worked with a number of partners using different alloys and copper types to measure the relative rate of copper dissolution. This work shows that some of the current alloy developments now offer superior performance to SnPb at the same temperature. Interestingly intermetallic formation between the alloy systems varies considerably. The copper type on the PWB is also influential,with significant differences between electroplated,electrodeposited and reverse treated.

Implementation of lead-free assembly processes results in higher copper dissolution rate than traditional SnPb alloys. The rate at which copper is dissolved could be dependent on many factors,such as solder alloy,contact time,solder temperature,flow rate,copper plating processes,copper grain structure,etc. The effect of assembly processes and process parameters on copper dissolution is well known and published. However,there is limited study on the influence of PCB (printed circuit board) fabrication processes and chemistries on copper dissolution.
This paper focuses on the effect of copper plating processes and chemistries on copper dissolution. Different Cu plating methods and chemistries were studied and compared. The paper will discuss the impact of Cu plating processes (direct current plating vs. pulse reverse plating),current density,plating chemistries and rectifiers on dissolution rate. The Cu microstructure from different plating methods is discussed.

The process of plating through holes (PTH) is inherent to modern PCB manufacturing. In an arena of increasing circuit density and layer counts,the reliability of the PTH process is under constant microscopic examination. The aim of electroless copper is to plate a conductive layer through a hole or into a blind microvia. In this context an interconnect (IC) refers to the copper to copper adhesion within the functional constraints of a circuit board. As these can include many inner layers,the inter connection quality is of prime concern. In addition the PTH process also inherits the issues from the preceding manufacture.
Some examples are highlighted below:
Base material
Material properties can result in significant Z axis mobility. Hybrid builds (different materials in one build) can be exceptionally
vulnerable and the problem is amplified in thicker panels.
Drilling
Drilling practices can affect smear residues and inner layer damage dramatically. Later processes can minimize the impact of
these but only if the manufacturer is aware of it. Unless the source of a type 1 inter-connection defect is clear,it is usually attributed to the PTH process employed.
Using electroless copper as an example,the impact of PTH on IC quality will be discussed. For this purpose it is useful to divide the PTH process into the following subsets:
- Desmear
- Cleaning/Conditioning
- Activation
- Electroless copper
This paper presents the impact of the individual PTH steps!

Fully automatic X-ray Inspection (AXI) is an established technique for inspecting component mounting and solder joint integrity on PCBA’s. It is occasionally used for the detection of faults on (or more precisely,under) press fit connectors. However,existing commercial automatic X-ray inspection systems limit the application of this technique to sample boards smaller than 610mm (24”) x 508mm (20”) and under 5mm (0.2”) thick. This is far too small an envelope to test most backplane assemblies and other large PCBA’s. These systems also use higher X-ray energies than is required to find all the types of assembly faults found on backplanes thereby unnecessarily increasing the weight and cost of the safety enclosures.
Existing manual systems can handle the largest of backplanes,but expecting a human operator to consistently recognise minor defects in the several hundred images required for a single large backplane (never mind production volumes) is unrealistic.
The authors describe a novel concept for a test system where a low energy micro focus X-ray source,and a 4 mega pixel detector,are mounted in separate robotically controlled heads. Each head is also fitted with a high resolution colour machine vision camera. The resulting RXI (Robotic X-ray Inspection) system provides both high resolution AXI for detecting faults under connectors,and full colour high resolution optical AOI for detecting faults within connectors,in the same machine,and in a single test activity. This fully automatic test system is a reliable,high speed,and highly cost effective test system for backplanes and other large PCB assemblies up to 1000mm (39.4”) x 1600mm (63”) in size and over 18mm (0.7”) thick.

Conformal coatings are used in high reliability electronics to protect the circuits from environmental contaminants. They are
applied by a variety of methods,and in varying thicknesses. Confirming that the thickness meets specifications called out by
documentation or customer can be problematic. Mechanical,ultrasonic,electrical (capacitive,eddy current),and various optical techniques are available,but all involve incurring significant limitations/penalties in capability,capacity or cost.
For optically transparent,and some translucent coatings,it is possible to accurately measure the thickness using optical (focal) techniques. This paper presents data on an innovative coating measurement process based on commercially-available low-cost optical equipment modified to make the measurements. The modified equipment is capable of making measurements on films as thin as 25µm (0.001”) and thicker than 1000µm (0.040”) with high repeatability. The method does not require a free edge and is not dependent on before/after coating differential measurement. The process has been fully developed and is used in a production environment.
The paper presents an overview of the equipment and method,Gage R&R data for the process,as well as comparative
information on other available techniques. The focal technique is applicable to measurement of all types of optically clear coatings and films,and is appropriate for moderate-volume measurement applications where direct,non-contact measurement of coated parts is desirable and where measurement in small areas is required.