Cleaning PCBs Only with Reliability Testing for Electronic Devices

Sources of PCB contamination can have a significant impact on the reliability and performance of modern electronic systems. With increasing demands for size reduction and enhanced intelligence of electronic systems, there is growing pressure to miniaturize components while ensuring their reliability and long service life. Modern printed circuit boards (PCBs) are complex, multilayered electronic components that require meticulous cleanliness to ensure the reliability of the final electronic product. Failures in these components caused by contamination are undesirable, making it crucial to pay attention to both PCB cleaning and cleanliness testing.

Contaminants in Manufacturing and Their Impact on PCBs

Sources of PCB contamination, particularly metallic impurities in solder, can significantly affect the quality and reliability of solder joints. Such contamination influences the joint's microstructure, mechanical strength, brittleness, wetting performance, and electrical properties, including electrical resistance. Soldering defects such as solder balls, dull solder surfaces, joint cracking, and insufficient filling of plated through-holes may also result from excessive contamination of the solder.

Sources of contaminants in solder and their dangers:

• Aluminium (Al): A small amount of Al dissolves in tin at elevated temperatures, leading to decreased adhesion, coarseness, higher solder viscosity, and potential surface oxidation.
• Antimony (Sb): Sb additives significantly improve wetting, limit whisker* growth, and eliminate tin whiskers. Simultaneously, they enhance solder strength.
• Arsenic (As): Harmful additive causing long needles in the microstructure and inducing non-wettability.
• Bismuth (Bi): Considered an alloying element, Bi improves wetting characteristics and results in positive changes in the lattice.

*Whisker: A thin, hair-like growth that can appear on the surface of metallic materials. Whiskers often form on solder surfaces, especially on soldered joints. These microscopic structures resemble fine hairs or needles and can gradually elongate.

Contaminants from Substrate and Components

• Iron (Fe): Iron contamination causes solder brittleness and coarseness.
• Other Metals: Many other metals (Mg, Ni, Au, Cu, Ag, Zn) form intermetallic compounds that can affect solder properties.

Sources of PCB Contamination During the Production Process

The sources of PCB contamination during the production process can include metallic layers on the substrate, dissolution of components, and impurities introduced during PCB processing and material dissolution. Additional sources, such as metal particles and residues, can contribute to impurities in solder and negatively affect the properties of solder joints.

Assessing and Controlling Contaminant Levels in Joints

Identifying the sources of PCB contamination and controlling the level of contaminants in solder joints are crucial steps in ensuring the quality and reliability of soldered joints on PCBs. High contamination levels can lead to serious issues with electronic components, emphasizing the need to select solder materials carefully and monitor the soldering process to minimize impurities.

Causes of Contamination

The sources of PCB contamination can be divided into two main categories: ionic and non-ionic contamination. Ionic contamination is often caused by flux residues and mainly consists of inorganic salts or acids. These residues can increase solution conductivity, creating conditions for corrosion and dendrite growth, ultimately leading to board failure. Non-ionic contamination includes non-conductive substances such as oils, inert flux residues, and greases.

Identifying Sources of PCB Contamination

Understanding the sources of PCB contamination is essential when investigating issues such as white spots or white residue caused by ionic contamination. These metal salts, acting as activators in fluxes, can cause reliability issues, especially when sufficient cleaning is not performed. Identifying the source of contamination is a necessary step in addressing the problem. Changes in processes, materials used, or cleaning solutions can lead to unexpected residues and cleaning challenges.

Choosing the Right Cleaning Fluid

Selecting the right cleaning fluid for printed circuit boards (PCBs) depends on several factors, including the type of contamination, PCB material, solder used, and the desired cleanliness level.

• Non-ionic Fluids

For removing non-ionic contamination, such as oils, inert flux residues, resins, and greases, non-ionic cleaning fluids are often recommended. These fluids are designed not to leave ionic residues that could affect conductivity on the PCB.

• Avoiding White Spots

To prevent white spots, often associated with ionic contamination, it is crucial to choose a cleaning fluid that is effective in removing flux residues while minimizing residues.

Choosing the appropriate cleaning fluid is crucial for effective cleaning. Modern cleaning agents with low viscosity and surface tension, capable of efficiently removing flux residues beneath densely populated components, are an ideal solution.

Verification of Cleaning Process through Inspection

Visual inspection is one of the simplest ways to assess board cleanliness. However, relying solely on visual inspection is not recommended, as some ionic contaminations are not optically visible. To identify the sources of PCB contamination and evaluate their impact on board reliability, more advanced testing methods are required. Methods such as Surface Insulation Resistance (SIR) testing or Ion Chromatography (IC) provide quantitative results and enable more efficient detection and analysis of contamination.

Surface Insulation Resistance (SIR) Testing and Ion Chromatography (IC)

SIR testing measures the reliability of electronic components by monitoring signal strength and quality after cleaning. IC is a common classification for evaluating PCB cleanliness, detecting weak organic acids, and individual ions. While ion chromatography may be more expensive, it provides the most reliable results for assessing board cleanliness.  More about the need and reasons for testing.

Cleaning even with No-Clean Solder Paste

Understanding the sources of PCB contamination, including residues from no-clean fluxes and soldering processes, is essential for ensuring the reliability of protective coatings and electronic assemblies. No-clean fluxes can hinder the proper adhesion of protective coatings on the board surface. This is a particular issue for boards exposed to harsh environmental conditions. Residues remaining after soldering can absorb moisture, which is released during curing and may cause the coating to separate from the board. Ensuring the complete removal of soldering residues can effectively prevent these problems.

Innovations in cleaning agents and testing methods bring significant improvements to the reliability and lifespan of electronic components. Modern cleaning processes not only provide higher-quality cleaning but also offer economic benefits for electronics manufacturers. With advanced cleaning capabilities, manufacturers can achieve higher PCB quality, ensuring the reliable operation of modern electronic devices.

At Gatema PCB, we place a strong emphasis on ensuring optimal reliability of electronic devices through innovative PCB cleaning processes. By understanding the sources of PCB contamination and their potential impact on electronic assemblies, our company applies targeted cleaning and reliability testing methods as a key element of our manufacturing processes. In contrast to traditional cleaning methods, our approach focuses on efficiency and effectiveness in eliminating contamination without compromising the integrity of the board or the environment.