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This paper extends our study of the sequential electrochemical reduction analysis (SERA) technique for evaluation of various alternative finishes and it discusses the application of the SERA technique to assess the surface conditions of the silver finish. The tarnishing products of the silver formed under ambient and artificially created conditions were analyzed, the protective effect of an anti‐ tarnishing film was evaluated, and the influence of the elevated temperatures (reflow) on the stability of the organic inhibitor and the formation of the tarnishing film will be shown.

As an alternative to hot air levelling, a fundamentally new surface finish chemistry and process for solderability preservation of printed circuit boards is described: a pretreatment of the copper followed by an optimized formulation of an immersion tin. The precise and reproducible surface finish formation offers reliable solderability, economic and technical advantages for all kinds of PCBs, even for those with the most modern miniaturized structures. The deposition chemistry and ageing properties of the new Organic Metal/tin surface is discussed, based on electrochemical, wet chemical and electron microscopy studies. The results culminate in an almost complete basic understanding of the tin chemistry and the surface finish performance.

This study seeks to examine the advantages of mildly alkaline immersion silver as a final finish for solderability in order to combat the shortcomings of acidity in some popular immersion silver solutions.

The paper describes in detail the necessary steps in the mildly alkaline immersion silver process.

The process can overcome the problems of conventional acidic immersion silvers, especially in thermal shock and stress testing. Also it does not affect soldering or aluminium wire bonding.

This is arguably a pioneering study in that it posits the benefits of mildly alkaline immersion silver as a final finish for solderability.

This work sets out to characterise the protective properties of conformal coatings and how they degrade.

The approach dosed several commercial coatings with two different contaminants, a synthetic generic flux mixture of dibasic acids in both a solvent‐ and water‐based carrier, and sodium chloride. The protective properties were monitored using three complementary techniques: surface insulation resistance measurements, sequential electrochemical reduction analysis, and diffusion measurements.

The experimental approach was verified and the SIR measurements were shown to be the most valuable. Coatings offered varying levels of resistance to the contaminants, with the silicone coating being the most resistant. The flux variants generally proved more harmful to the coatings, suggesting that flux diffusion through the coating exceeded that of NaCl and hence led to greater electrochemical corrosion. Flux transmission through the coatings was verified by the diffusion measurements.

The project only investigated a limited number of contaminates on simple single sided boards. Future work will investigate coverage effects and a wider range of contaminants.

The work shows that coatings can allow diffusion of contaminates, particularly organics, which can lead to corrosion. The test methodology described here can be used to characterise coating susceptibility.

This work starts to develop for the first time a test methodology to characterise the protective properties of conformal coatings, and shows that flux, and hence other similar organic contaminants, may represent a protection challenge for some coating chemistries.

To present a new tin plating process which provides deposits having a fine‐grained structure and stable crystal orientation with a combination of properties which are well suited for use as a lead‐free finish on semiconductor lead‐frames.

The new process was designed to produce tin coatings with a deposit grain size ca 20 per cent that of a traditional matte pure tin finish to ensure that the deposit retains good solderability after steam ageing.

The enhanced solderability from the finer‐grained deposit has been demonstrated and other functionally important deposit properties have been confirmed. A stable single crystal orientation 〈220〉 indicates low whiskering propensity and measurements have confirmed the excellent whisker performance, even without specific whisker‐preventing countermeasures. The deposit has high ductility. Analytical methods are available for all key components to ensure optimum process control. The process has been tested in a continuous production environment for over 12 months with excellent results.

The novel process described in the paper provides tin deposits having a unique combination of properties and with production‐proven capability to be an ideal lead‐free solution as a solderable finish for electronic components.

To investigate the relationship between intermetallic compound (IMC) formation and solderability for immersion tin deposit under different number of reflows.

Scanning Auger microscopy and X‐ray photoelectron spectrometer surface analysis techniques were used to study changes in immersion tin deposit layer when subjected to simulated solder reflow conditions.

Auger analysis also showed that no three discrete uniform layers of pure tin, Cu₆Sn₅η‐phase and Cu₃Sn ε‐phase can be observed after one reflow. Degradation in solderability performance after reflow was due to the formation of a Cu₆Sn₅ IMC at the surface. This IMC has inferior solder wetting properties compared to tin. As the number of reflow cycles increases the surface contains less tin rich regions and more IMC regions. Experiments showed that longer reflow times during the assembly process or use of a thicker tin layer can improve the solderability after three reflow cycles.

This work has shown that longer reflow times during the assembly process or use of a thicker tin layer can improve solderability after three reflow cycles. These two approaches are thus recommended when using immersion tin finishes on PCBs that require multiple lead‐free reflow cycles.

This paper provides valuable data that will assist PCB assemblers to optimise their solder reflow conditions when assembling boards that require multiple solder cycles.

An overview has been presented on the topic of alternative surface finishes for package I/Os and circuit board features. Aspects of processability and solder joint reliability were described for the following coatings: baseline hot‐dipped, plated, and plated‐and‐fused 100Sn and Sn‐Pb coatings; Ni/Au; Pd, Ni/Pd, and Ni/Pd/Au finishes; and the recently marketed immersion Ag coatings. The Ni/Au coatings appear to provide the all‐around best options in terms of solderability protection and wire bondability. Nickel/Pd finishes offer a slightly reduced level of performance in these areas which is most likely due to variable Pd surface conditions. It is necessary to minimize dissolved Au or Pd contents in the solder material to prevent solder joint embrittlement. Ancillary aspects that include thickness measurement techniques; the importance of finish compatibility with conformal coatings and conductive adhesives; and the need for alternative finishes for the processing of non‐Pb bearing solders are discussed.

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 purpose of this paper is to investigate the oxidation behaviour of an immersion tin final finish after multiple reflow ageing under air and nitrogen atmospheres and to study their influence on the wetting behaviour with lead‐free solder. To design a model that describes the degradation of wetting behaviour after reflow‐cycling of the immersion tin final finish.

A special printed circuit boards (PCB) demonstrator was created to investigate the immersion tin final finish with surface analysis methods and wetting tests. The PCB samples were aged by multiple reflow‐cycling under air and nitrogen atmospheres. The tin oxide formation behaviour of immersion tin was characterised using X‐ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and SERA analysis.

The native oxide layer of the investigated immersion tin final finishes was approximately 7 nm on average. The TEM and XPS investigations indicated an amorphous structure of SnO and SnO₂. The solder spread test showed significantly different results for PCBs in “as received” condition compared to those after one and two times reflow ageing under a nitrogen solder atmosphere. The analysis methods revealed a slight increase in the tin oxide layer thickness and small areas with semi‐crystalline structure. Reflow ageing under an ambient solder atmosphere induced considerably thicker oxide layers, which could be observed by a yellow discoloration of the surface.

Measures to improve the wetting behaviour can be derived from the described model (i.e. use of higher tin layer thickness or protective films to reduce the tin oxidation).

A functional model for the solderability process of lead‐free solder on immersion tin PCB final finishes was derived and verified. By this, interactions between the state of the final finish and the solder can be described and potential solderability failures can be predicted.