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The purpose of this paper is to detail progress on the European Commission supported FP7 ASPIS project that is undertaking a multi‐faceted approach to develop novel and improved nickel‐gold (ENIG) solderable finish chemistries and processes in order to overcome issues such as “black pad” that are known to cause reliability issues.

The ASPIS project has four key and discrete approaches; research into “black pad” formation mechanisms, development of new aqueous chemical deposition methods, formulation of new processes based on ionic liquids and the development of prognostic screening tools to enable early prediction of reliability issues.

Key factors influencing “black pad” formation include immersion gold bath pH value, concentration of citrate and thickness of the immersion gold layer. In addition, copper substrate preparation is also important. Work to develop new metal deposition processes using ionic liquids has also been demonstrated and may provide a viable alternative to more conventional aqueous based chemistries, thereby enabling some of the conditions that lead to “black pad” to be avoided.

This paper summarises the work carried out in the first year of a three‐year project and so the outputs to date are relatively limited. The project is continuing for another two years, when further progress will be made. It is hoped to report this progress in a future update paper.

The ASPIS project has undertaken multiple approaches to the development of new high reliability nickel gold finishes and this combination of approaches should offer synergies over more discrete traditional methodologies. As well as undertaking a detailed analysis of the mechanisms causing reliability problems, radical new formulation and prognostic approaches are also being developed.

Studies immersion gold over electroless nickel, immersion gold over electroless palladium, immersion gold over electroless palladium over electroless nickel, immersion gold over immersion silver and immersion silver. In the palladium finishes, two palladium thicknesses were evaluated: 10‐12μin. and 18‐20μin. Multiple plating chemistry suppliers provided plated test vehicles. HASL and OSP test vehicles were included as control samples. In total, 14 finishes were evaluated in the test matrix. The test vehicle was a daisy chain of zero ohm 1,206 chip resistors that could be monitored individually. Test vehicles were assembled using 63Sn/37Pb eutectic solder paste on an automated assembly line. The thermal cycle range was ‐40°C to 125°C with 30‐minute transition times and 15 minutes at each extreme in a single chamber air system. For each test matrix cell, 120 zero ohm resistors (40 from three boards) were continuously monitored for electrical failure (>100ohms). In addition, resistors were sheared from test vehicles and the shear force at failure was recorded. A decrease in shear force did occur with thermal cycling due to crack initiation and growth in the solder joints. Solder joint cracks have also been examined.

The aim of this paper is to detail the changes needed to ensure compatibility of printed‐circuit board (PCB) surface finishes with the use of lead‐free solders and in lead‐free assembly processes.

The paper describes the various popular solderable surface finishes that are currently available. It then reviews them in terms of the required adaptations necessary to meet the requirements of the Restriction of Hazardous Substance (RoHS) Directive and to ensure compliance, whilst meeting the performance needs of the product.

Some of the available and popular finishes, such as organic solderability preservatives and tin require modifications while, others including silver, direct immersion gold and electroless nickel immersion gold are transitioning well into the world of lead‐free. Electroless nickel, electroless palladium, immersion gold is one finish that performs better with lead‐free assembly than it did with conventional eutectic solder‐based approaches.

The paper provides a concise overview of the implications for specific surface finishes when making choices for use with lead‐free and RoHS compliant PCB soldering and assembly.

A problem exists with electroless nickel/immersion gold (E.Ni/I.Au) board surface finish on some pads, on some boards, that causes the solder joint to separate from the nickel surface, causing an open circuit. The solder joint cracks and separates when put under stress or when it experiences a shock. An ITRI (Interconnect Technology Research Institute) project to investigate this E.Ni/I.Au problem was initiated about a year‐and‐a‐half ago. Since the electroless nickel/immersion gold board finish performs satisfactorily most of the time, a 24 variable experiment was developed to investigate which parts of the chemical matrix are satisfactory to use and which need to be avoided. This paper describes some of the activities that have occurred on the ITRI consortium, from the design of the test vehicle to building hundreds of BGA assemblies, then pulling those BGA assemblies apart and inspecting the results.

The use of an electroless nickel/immersion gold (ENIG) surface finish comes with the inherent potential risk of Black Pad failures that can cause fracture embrittlement at the interface between the solder and the metal pad. As yet, there is no conclusive agreed solution to effectively eliminate Black Pad failures. The case studies presented are intended to add to the understanding of the Black Pad failure mechanism and to identify both the plating and the subsequent assembly processes and conditions that can help to prevent the likelihood of Black Pad occurring.

Scanning electron microscope (SEM) analysis of exposed pad surfaces on failed PCBs demonstrated a “mud‐crack” appearance, which is a characteristic of the Black Pad phenomenon. In addition, energy dispersive X‐ray (EDX) analysis was used to identify the elemental composition of the fractured layer between the Ni₃P and Ni₃Sn₄ inter‐metallic compound, confirming the presence of Black Pad.

Grain boundaries or “mud‐cracks” that can be clearly seen in a top view of the failed pad surface and corrosion spikes in the failed pad surface, as evident from the cross‐section sample, should be used as a guideline to confirm Black Pad failures. Maintaining an optimum and well‐controlled EN and immersion gold bath, in addition to good process control prior to nickel‐gold deposition is recommended as the best approach for minimizing the occurrence of Black Pad failures.

Only Sn/Pb soldering processes using ENIG PCBs or package substrates were evaluated and discussed. Thus, the current case studies do not encompass Black Pad failures with lead‐free soldering.

The work reported provides guidelines that can be used to identify Black Pad occurrence. It also proposes relevant approaches for minimizing the possible occurrence of Black Pad.

The findings of these studies provide a basic understanding of the Black Pad failure mechanism. Subsequently, both the plating and the ensuing assembly processes and conditions that can help to prevent the likelihood of Black Pad occurrence were identified.

Nickel–gold planar surface coatings have been increasingly specified over the last ten years as the circuit board solderable finish of choice. Although offering a number of significant advantages over both conventional Hot Air Solder Levelled (HASL) finishes and alternative planar finishes, nickel–gold can, under certain conditions, be associated with a premature brittle interfacial solder joint fracture failure. This failure typically occurs at the interface of the nickel deposit and the intermetallic formed during soldering. The exposed nickel usually exhibits a “blackish” discolouration that has led to the term “black pad” being used to describe such failures. Although black pad usually occurs at very low levels, its incidence can be catastrophic and hence much work has been done by numerous workers to elucidate further the causes and mechanisms of this failure. This paper reviews the current understanding of the black pad failures and details work carried out by Shipley to extend this knowledge and to help users minimise the likelihood of its formation.

The purpose of this paper is to present a better understanding of nickel corrosion, also known as “black pad” during gold deposition of EN1G.

This paper presents an accumulation of personal experience and observations of the problem over a period of ten years. It incorporates the experience of the Global Trade Association connecting the electronic industries (IPC) plating committee as it set out to write the IPC electroless nickel‐immersion gold (ENIG) specification‐4552.

Understanding how corrosion occurs will go a long way in helping printed circuit board (PCB) manufacturers stay clear of the issue and make high quality ENIG finished PCBs.

The majority of the data presented has been substantiated.

The paper details how, by good understanding of the mechanism of formation of corrosion products, manufacturers can steer clear from the problem.

Printed circuit boards (PCBs) requiring component attachment, whether leaded or surface mount technology, must have the exposed copper land areas coated with a protective finish. This protective coating must not inhibit solderability and at the same time must act as a barrier for preventing the copper from oxidizing and the inevitable assembly problems that would ensue for the end‐user. Globally, the predominant surface finish in the PCB industry is hot air solder levelling (HASL). Driven by the adoption of solder mask over bare copper, HASL was developed as a reliable method of applying solder to the copper surfaces after solder mask. During HASL, a thin layer of solder is deposited onto the exposed copper by passing the boards through a hot, molten wave (or pot) of solder and subsequently blowing the excess solder from the boards using high velocity hot air. This process has been increasingly under scrutiny due to environmental and safety issues (hazardous waste, lead exposure, etc.), technological limitations (fine‐pitch device assembly) and equipment maintenance cost. This paper reviews the major alternative surface finishes being currently deployed and additionally seeks to give an overall assessment of the broader environmental aspects of such finishes.

The purpose of this paper is to present the optimisation of protocols for the immersion coating of silver onto copper‐track printed circuit board (PCB) assemblies, using a novel class of ionic liquid and to show the implementation of the scale up process.

Various conditions (temperatures and silver concentrations) are studied individually under laboratory conditions and then optimised for a pilot scale demonstrator line that is used to process British Standard test coupons.

The use of these novel liquids for the immersion coating of silver produces silver dip coatings that are bright and even and which give solderability that is as good as the commercial aqueous, nitric acid based, electroless process without any solder‐mask interface etching.

The combined technology has been optimised for an immersion silver coating line. Further development work should be undertaken to tailor the technology for gold immersion coating of PCB assemblies.

The paper details a process in which no solder‐mask interface etching is observed; that does not require the use of strong inorganic acids or expensive catalysts to sustain deposition and which does not appear to be light sensitive in contrast to other processes.