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4 years ago

EPP Europe P1.2020

  • Text
  • Assuraance
  • Test
  • Production
  • Assembly
  • Packaging
  • Printing
  • Process
  • Technologies
  • Automation
  • Manufacturing

PCB + ASSEMBLY

PCB + ASSEMBLY Fundamentals needed for a critical cleaning PCB cleaning – if you fail to plan, you are planning to fail The printed circuit board (PCB) is one of the most important elements within the design of an electronic product. As the heart of any electrical device, many features have to be considered to create a reliable and cost-effective board. Everything from determining the overall size and layout and whether it can accommodate all the components and signal tracks, to establishing what flux or paste to use. Will no-clean solder be the most effective solution, or a rosin or water-soluble paste? All of these factors have to be considered during the design stage and planned before PCB prototyping or production starts. One essential aspect however which is frequently overlooked during design is the critical process of cleaning the PCB to ensure reliability. Emily Peck, Senior Chemist, MicroCare Corporation PCB cleaning decisions should be made before prototyping or production starts. Cleaning can quite often be an afterthought once the initial design of the PCB has been planned. Or it may come into question as the planning process nears completion after important decisions about coatings, solder pastes and other materials have already been finalised. This results in a PCB that looks the part but performs poorly and is vulnerable to failure resulting in product recalls and costly returns. It can also have a substantial effect on manufacturing schedules, as designers seek answers to malfunctioning boards and post-production cleaning solutions to rectify the problem. Source: MicroCare Corporation Cleaning early in process Early planning is key for PCB manufacturing success and is becoming more significant with the continuing miniaturisation of components. The push to downsize has been driven by several industries particularly for medical applications and within the automotive sector with autonomous and intelligent transport systems advancing at speed. Because of the increasing need for sophisticated electronics, PCB designers are recognising the benefit of specifying their cleaning choices earlier in the design process, as they understand that one of the main causes of electronic device failure is contamination on the PCB. It is very often simpler to detect and rectify any cleaning problems before the prototyping and production stages. This is particularly true when manufacturing high-reliability PCBs such as those used within the military industry, or in medical devices like pacemakers where cleanliness is not just critical, it is a matter of life or death. Designers are starting to change their mindset by taking a proactive approach to PCB cleaning. They recognize the importance of successful cleaning and are stipulating cleaning details in the early stages of PCB design. Early identification of contamination The use of smaller PCBs filled with densely placed components makes managing faults problematic and cleaning a challenge. It is important to first identify the contaminant. There are two forms of contamination found on a PCB, ionic and non-ionic. Ionic contamination is most typically flux residue left behind during the manufacture of the board, or after the soldering process – and is usually inorganic salts or acids. This ionic residue contains molecules that are conductive when in a solution. If it is exposed to levels of moisture, the ionic residue can split into negatively or positively charged ions increasing the overall conductivity of the solution. If left untreated, it will degrade and may lead to corrosion and dendrite growth causing leakage and short-circuits, ultimately resulting in the failure of a device. The risk of malfunction increases further if a conformal coating is being used. Trapped moisture absorbed by the flux residue may be released during curing operations, causing the conformal coating to 30 EPP EUROPE April 2020

separate from the board. This can allow corrosive materials, dust, or water to penetrate the PCB leading to an array of potential problems. It is therefore important for the PCB designer to choose an appropriate flux remover to clean any residue from the boards. Selecting a cleaning process that works Once the contaminant has been determined during the planning stage, the next question to ask is what cleaning fluid and method should be used? Effective cleaning ultimately contributes to the functionality and reliability of the board but it has to be performed using a process that will not damage the PCB. Components can be loosened, connections broken and substrates impacted if the wrong cleaning fluid or inappropriate cleaning method is used. For example, a strong cleaning fluid can dissolve plastics or other soft materials on the PCB. If a high-pressure spray is used to clean under low-standoff components, it could displace delicate components. The fluid used to clean a PCB has to be compatible with a variety of substrates, without damaging any coatings, yet strong enough to successfully remove the flux residue. The cleaning fluid needs to be matched to the contaminant to effectively clean without compromising the board. Pre-testing – the answer to successful PCB production Fundamental to PCB design is pre-testing. Understanding how to clean all the elements of the PCB early in the design process must be investigated. By instigating test cleaning at the initial concept stage, designers have an understanding of how their choices of pastes, fluxes and cleaners impact the performance of the board. Zusammenfassung Die Leiterplatte (PCB) ist eines der wichtigsten Elemente beim Design eines elektronischen Produkts. Ein wesentlicher Aspekt, der jedoch während der Entwurfsphase des Designs häufig übersehen wird, ist der kritische Prozess der Reinigung der Leiterplatte, um deren Zuverlässigkeit zu gewährleisten. Résumé Le circuit imprimé (PCB) est l’un des éléments les plus importants de la conception d’un composant électronique. Bien qu’il soit souvent négligé pendant la phase initiale de la conception, le processus de nettoyage du circuit imprimé est critique et essentiel pour garantir la fiabilité du circuit. Резюме Печатная плата (PCB) является одним из важнейших элементов при проектировании электронного устройства. Однако ключевым аспектом, который часто упускается из вида на этапе проектирования, является процесс очистки печатной платы, критически важный для обеспечения ее надежности. Protect your customers against negative surprises. High-end quality assurance in series. With ultra-precise test systems from MCD. Our electronical measurement and test systems cover the whole range of applications. From optic, accustic, haptic to sen soric realizations. Whether customized or out-of-the-box - MCD offers scalable solutions up to integration to industrial assembly line production. EPP EUROPE April 2020 31 www.mcd-elektronik.com