Does lead roughness correlate to corrosion content?

The electronics industry perceives corrosion on soldering leads as a potential risk to the solderability of the components.¹ Several traditional methods assess the solderability of an electronic component.² In the defense industry, samples from a component batch that is suspected of poor solderability must be inspected according to MIL-STD-202, Method 208,³ and SAE 2626² used in the automotive industry. Typically, samples of the tested components are selected and tested under specified conditions to gauge solder wettability on the component leads and the bond strength. The current procedure is practiced on a very small sample of components within a batch under the assumption that few samples represent the entire batch. This is not the case, however.⁴ Yet, the effect of corrosion on soldering leads on product quality is rarely considered, despite numerous evidence and research on the impact of corrosion on the bond strength and its reliability.^5-8

Imaging of hidden solder pastes under MLF-100s revealed joint and voiding formation mechanisms differed from each of the solder pastes evaluated.

SnPb (tin/lead) is considered the most reliable solder alloy for aerospace/defense (IPC Class 3) applications because of its ability to withstand shock and vibration and mitigate Sn whiskering. SnPb components, however, are becoming obsolete from increasing restrictions of Pb in commercial applications. Presently waived for AD, these solders are increasingly expensive, with increasing supply constraints and reliability limitations. Moreover, current SAC 305 alloys also fall short of commercial performance objectives, especially in automotive (electric vehicle) end-use environments. As a result, the Raytheon Lead to Lead-Free (L-LF) team evaluated two current baselines and seven next-generation LF solder paste alloys based on three major “pathfinder” studies on representative SMT assembled test samples, to identify the best LF alloys for the next phase for production prototypes. An L-LF working subgroup was formed to outline a path forward to better anticipate and prepare the transition to a “pure” LF metallurgical system for circuit card assemblies (CCA). Raytheon has been successfully mixing SnPb paste and LF SAC 305 parts with ~225°C processing temperatures without having to reball from SnPb to Pb-free; this is ~15% of product today. The strategy is to transition from SnPb to next-generation Pb-free solder paste alloys to mix-assemble with SAC 305 or Sn surfaces between 200° and 240°C or melting ranges between 183° and 220°C for minimum transition disruption, but not too low; e.g., low-temp (~150°C) solders (LTS) that risk reflowing material with lower temperature processing used in subsequent next higher assemblies (NHA) (FIGURE 1).

The actual phosphorus content in the deposit must be considered.

While the current focus in the electronics industry is chips, components and microelectronics, the printed wiring board (PWB) also plays a vital role. Continued miniaturization and environmental considerations, such Restriction of Hazardous Substances Directives (RoHS), have led the industry to create and improve surface finishes to meet current and future generations of electronic assemblies. Two PWB finishes have become very common: ENIG and ENEPIG. The industry trade association, IPC, released IPC-4552 in 2002¹ to help standardize the global printed circuit board industry around a specification for ENIG. IPC-4556 was released in 2013² to establish industry standards around ENEPIG surface finishes.

Following its acquisition of ACI, APCT head Steve Robinson is bullish on what's ahead.

APCT in February completed the acquisition of Advanced Circuits Inc. (ACI), a printed circuit board fabricator based in Aurora, CO, and with facilities in Chandler, AZ, and Maple Grove, MN. The acquisition nearly doubles APCT's annual revenue to $200 million, and makes the company the third largest among PCB fabricators in North America behind TTM and Summit Interconnect.

In March, Steve Robinson, president and CEO of APCT, joined PCEA president Mike Buetow on the PCB Chat podcast to discuss the acquisition, the pending integration, and APCT's new responsibilities as one of the largest North American PCB fabricators. This transcript has been lightly edited for grammar and context.