A comparative analysis of printed circuit drying methods for the reliability of assembly process. (February 2022)

• Record Type: Journal Article
• Authors: Ciszewski, Piotr; Sochacki, Mariusz; Stęplewski, Wojciech; Kościelski, Marek; Araźna, Aneta; Janeczek, Kamil
• Is Part Of: Microelectronics and reliability. Volume 129(2022)
• Publication Date: 2022-02
• Subjects: Drying -- Flex -- Rigid-flex -- Semi-flex -- Printed circuit boards; Electronic apparatus and appliances -- Reliability -- Periodicals; Miniature electronic equipment -- Periodicals; Appareils électroniques -- Fiabilité -- Périodiques; Équipement électronique miniaturisé -- Périodiques; Electronic apparatus and appliances -- Reliability; Miniature electronic equipment; Periodicals; 621.3815
• DOI: 10.1016/j.microrel.2022.114478
• Languages: English
• ISSNs: 0026-2714

Abstract

Abstract: Aim of the research was to examine the effectiveness of various methods to remove moisture from printed circuit boards (PCBs) depending on PCB's type and process parameters. The presented results are part of ongoing research on the absorption and desorption of moisture. The additional aim is to find new solutions to increase the reliability of electronics. The results are useful for whole EMS market because they facilitate to select the most appropriate method for their products. The initial conditions and parameters of the process are selected to reduce the risk associated with high temperature annealing while preventing damage caused by moisture during soldering. The FLEX, RIGID-FLEX and SEMI-FLEX PCBs were fabricated. All PCBs were humidified and exposed to drying conditions in which elevated temperature, reduced humidity or reduced pressure were utilized. The parameters were set by taking into account material characteristics, process time and operation cost. Mass of the samples was measured before and after annealing so as to evaluate the removed moisture. The highest removal rate was observed at the beginning of the drying. The recommended time was appeared to be 8 h. The most efficient method was high temperatures annealing, but it should be taken into account that the treatment can result in micro-damages and aging. It is recommended to limit repetitions of the process as well as to store PCBs at temperature in the range of 20–25 °C and humidity below 5% RH. An alternative is an annealing at reduced pressure and elevated temperature or application of anaerobic chamber with nitrogen and moisture below 0.5 ppm. Highlights: Duration of moisture removal from FLEX/RIGID-FLEX/SEMI-FLEX PCBs using different methods of drying does not exceed 8 hours. 8-hour drying is a compromise between the residual moisture and the impact of annealing on solderability and reliability. Humidity of 5% RH slows down efficiently the process of removing moisture from PCBs at temperatures above 100 °C. Reduced pressure at elevated temperature (drying in anaerobic chamber) is an alternative to annealing at temperature of 100 °C The drying in a vacuum is three times cheaper than annealing the cost of which is similar to drying in a nitrogen chamber. The drying in a climatic chamber is up to ten times more expensive than drying in an annealing chamber.