Technical Library

IPC J-STD-004B standard prescribes general requirements for the classification and testing of soldering flux for high qualify interconnections. This standard defines the classification of soldering materials through specifications of test methods and inspection criteria. The materials include liquid flux, paste flux, solder-paste flux, solder preform flux, and flux-cored solder.

The Connected Factory Exchange initiative enables the use of tools, machines, and computer software to monitor, improve, and produce reliable hardware. The concept of the Digital Twin is to connect and communicate with assembly machines to analyze data, and from the data analytics, adjust and control the process.

J-STD-001G Amendment 1 standard requires an OEM and EMS to qualify soldering and/or cleaning processes that result in acceptable levels of flux and other residues. Objective evidence shall be available for review. The use of the historical 1.56 μg/NaCl equivalence/cm2 value for ROSE, with no other supporting objective evidence, is not considered acceptable for qualifying a manufacturing process.

Since the 1970s, ROSE testing was used to determine “clean enough.” In 2015, the J-STD-001 committee assigned a team to develop the next generation of “cleanliness” requirements. Section 8 defines the key concepts that drove the need for developing new cleanliness requirements.

Cleanliness is a product of design, including component density, standoff height and the cleaning equipment’s ability to deliver the cleaning agent to the source of residue. The presence of manufacturing process soil, such as flux residue, incompletely activated flux, incompletely cured solder masks, debris from handling and processing fixtures, and incomplete removal of cleaning fluids can hinder the functional lifetime of the product. Contaminates trapped under a component are more problematic to failure. Advanced test methods are needed to obtain “objective evidence” for removing flux residues under leadless components.

The functional reliability of electronic circuits determines the overall reliability of the product in which the final products are used. Market forces including more functionality in smaller components, no-clean lead-free solder technologies, competitive forces and automated assembly create process challenges. Cleanliness under the bottom terminations must be maintained in harsh environments. Residues under components can attract moisture and lead to leakage currents and the potential for electrochemical migration.

Recent electronic assembly innovations have produced more performance using highly dense interconnects (HDIs). However, solder paste and flux residues from the assembly process may increase the risk of premature failure or improper functionality. The challenge for OEMs is to qualify products that meet the mean time to failure reliability requirements. To do so, OEMs must understand “how clean is clean enough” under various levels of bias and environmental conditions. High density interconnects render this assessment more challenging as conductors and circuit traces are increasingly narrower.

The process cleaning rate theorem holds that the static rate (chemical forces) plus the dynamic cleaning rate (mechanical forces) equals the process cleaning rate. New lead-free flux residues result from more demanding soldering drivers created by high soldering temperature, surface tension effects, and miniaturization. Lead-Free flux compositions require thermal stability, resistance against burn-off, oxidation resistance, oxygen barrier capability, low surface tension, high fluxing capacity, slow wetting, low moisture pickup, high hot viscosity, and halogen free. The static cleaning rate for lead-free flux residues is dramatically different from eutectic tin-lead flux residues. To clean lead-free soils, longer wash exposure time, high cleaning agent concentrations, and high levels of mechanical energy are needed. The purpose of this research paper is to measure the cleaning variability induced by lead-free flux residues and to compare the cleanability of lead-free flux residues to determine the viability of new cleaning agent designs

Moore’s Law infers that the number of transistors on a chip doubles approximately every two years. Consistent with Moore’s Law, high reliability electronic devices build faster processing speed and memory capacity using increasing smaller platforms. The trend toward highly dense assemblies reduces the spacing between conductors while yielding a larger electronic field. As the industry moves to higher functionality, miniaturization, and lead-free soldering, studies show that cleanliness of the assembly becomes more important. Residues under low standoff components, with gaps less than 2 mils, represent an increasingly difficult cleaning challenge. Collaboration from cleaning equipment and cleaning material companies has led to innovations for improving throughput and complete residue removal under low standoff components. The purpose of this paper is to report both mechanical and chemical innovations that open the process window.

The job of a cleaning agent is to remove an unwanted contaminant, or simply some kind of “dirt”. How can you efficiently remove that soil while minimizing total waste and improving worker safety? While that answer evolves based on updated impact studies and new regulations, the goal of removing those undesired contaminants remains fixed. Responsible environmental stewardship challenges businesses to continuously evaluate safer or preferred process alternatives. Such as reducing waste or selecting products that are safer for their employees and the environment. This paper investigates a methodology for developing new processes that achieve the required cleaning effectiveness while balancing the environmental, human, and machine impacts for longevity

Since the development of Surface Insulation Resistance (SIR), an emphasis has been placed on utilizing a few “standard” test patterns, namely the “Y” test pattern and interdigitated “comb” patterns. These designs have historically lagged “leading edge” PCB design rules and even typical PCB design rules. These patterns share a common feature: they are “spherical cows,” meaning they are a highly simplified model of a complex phenomenon. The long, uniformly spaced, parallel electrode shape of the “Y” and “comb” patterns allows for the assumption of a uniform electric field. This means that the force imparted on an ion between the test patterns is independent of its location. However, this approximation is not valid when applied to modern components.

This paper is a continuation on an investigation into the mechanism(s) of metallic corrosion in the cleaning process. With the increased demand placed on increasing the reliability and functionality of Printed Circuit Board Assemblies (PCBAs) while at the same time decreasing the size and environmental impact manufacturers are having to use new materials and reevaluate reliability. One way to increase reliability is by cleaning the PCBAs to remove contamination, such as flux residues, which can cause or at least contribute to, numerous failure mechanisms. The combination of new materials and the need for cleaning to ensure reliable end products, which may have to have a lifetime of 25+ years in harsh environments, is leading to questions about the impact that the cleaning process has on PCBAs.

The activity of flux residue changes, when trapped under low profile leadless or bottom terminated components. There are three factors to consider: 1.) Standoff gap – Lower standoff gaps block outgassing channels. Low standoff gaps change the nature of the flux residue by leaving behind flux activators, solvents, and functional additives that normally would be outgassed from the residue. 2.) Narrow Pitch – Miniaturized components have a decreased distance between conductors of opposite polarity. There is a higher potential to bridge conductors with flux residue. 3.) Cubic Volume of Flux – Increased I/O in combination with thermal lugs creates a higher cubic volume of flux left under the bottom termination. High flux volumes can block outgassing channels and bridge conductors.

Electronic devices are essential to the reliable operation of the products that employ them. Miniaturization necessitates a fundamental change in how materials and processes are selected to ensure reliability. Solder is a critical component engineered for specific applications. Numerous factors require consideration including board finishes, solder alloy, reflow temperatures, and operating temperature. When process residues are cleaned, the interaction of the cleaning agent with exposed metals must also be considered

Two of the three primary cleanliness test methods for PCBs, Resistance Of Solvent Extract (ROSE) and Ion Chromatography (IC), rely on the assumption that all ionic contamination on a PCB will be soluble in a solution of 75% isopropyl alcohol (IPA) 25% De-ionized water (DI). This assumption is made in the most critical step of an analytical procedure, the extraction step. If this extraction step is not functional or even optimal, then no instruments further down the logical path can correct for poor extraction and you will not know the actual contamination levels on the PCBA. This is why, in many analytical textbooks, extraction studies are covered in the first few chapters, as poor extraction efficiency is the death of an analytical method.

Electronic device reliability is more challenging due to various factors related to increased functionality, component miniaturization and design, electrification, assembly process, and the demands of the user environment. Factors such as ambient humidity and temperature conditions, day/night temperature variations, cleanliness of the electronic circuitry, PCBA design, and surface characteristics all influence device reliability

Dr Mike Bixenman presents the variety of updates and improvements to the Magnalytix SIR tester, making the system easier to use and integrate into the production process.

As components reduce in size, the electrical clearance between conductors creates a reliability concern when flux residues are present. Since the area under these components is tiny, chemical extraction is no longer a reliable method for determining cleanliness levels. This problem finds a growing need to understand the impacts of residues left from the flux and other process chemistries on site-specific components. Since these residues can lead to premature failure of assemblies once in the field, an electrical test method on site- specific components and their response to the environment is needed.

The steady drum beat of miniaturization is driven by the insatiable demands of consumers for ever smaller, ever more capable, ever more reliable hand help and portable devices. These market moving trends have pushed technology development for the past few decades, and show no signs abatement. The combination of these requirements: smaller size, more capable, and more reliable are creating new demand for effective cleaning technology that heretofore was seen more commonly in military applications.

Material and Process Characterization studies can be used to quantify the harmful effects that might arise from solder flux and other process residues left on external surfaces after soldering. Residues present on an electronic assembly can cause unwanted electrochemical reactions leading to intermittent performance and total failure. Components with terminations that extend underneath the package can trap flux residue. These bottom terminated components are flush with the bottom of the device and can have small solderable terminations located along the perimeter sides of the package. The clearance between power and ground render high electrical forces, which can propagate electrochemical interactions when exposed to atmospheric moisture (harsh environments).

Highly dense printed circuit board assemblies (PCBAs) build in more functionality using leadless components. Over the past several years, bottom terminated components (BTCs) have continued to gain popularity and usage for their signal integrity, thermal, and power dissipation properties. While these packages offer gains in electrical functionality, they also pose challenges to ensure high quality and high-reliability operation. Thermal pads, thermal vias, and spacings between power/ground domains present unique challenges for the package type. One of those challenges is the risk of dendritic growth, leading to power-to-ground shorting or unwanted leakage currents. The condition may occur if unactivated flux residues remain between a BTC device and the printed circuit board after soldering.

In the design and development of safe, effect devices, reducing risk, and ensuring reliability are a manufacturer’s first responsibility. The advanced technology inherent in Class 3 hardware and their production means that all aspects of the system – including mechanics, electronics, software, and hardware must be evaluated for reliability. Every aspect of its development – from design and prototyping through manufacture, distribution, disposal, and decommissioning must adhere to strict quality standards that are documented and traceable to functional and safety requirements.

OEMs (Original Equipment Manufacturers) and EMSs (Electronic Manufacturing Services) work to a set of guidelines and test procedures for qualification of hardware when changing soldering materials, process conditions, cleaning materials, cleaning machines, and conformal coating. Evaluation and use of any soldering material, reflow setting, or cleaning material, the EMS shall confirm that the proposed materials are characterized and qualified to the applicable ANSI/IPC Industry Standards. Additionally, IPCJ- STD-001G, Amendment 1 issued changes to Cleanliness Standards requiring the assembler to develop objective evidence that a specific cleanliness condition renders a reliable device..