How does moisture cause huge problems on printed circuit boards?
By being present in the epoxy glass prepreg, diffusing in the PCB during the stored procedure, moisture can form various defects in the PCB assembly during absorption.The wet process time of the PCB manufacturing process exists in the microcracks or can form a home in the resin interface.Because the high temperature and steam pressure are parallel to the lead-free mechanism in the PCB assembly, this results in moisture absorption.
As failures of adhesives and cohesion in printed circuit boards lead to lamination or cracking, moisture can make metal migration possible, resulting in a low impedance path of dimensional stability changes.With the decrease of vitrification transition temperature, the increase of dielectric constant and other technical damages, it will lead to the decrease of circuit switching speed and the high propagation time delay.
The main effect of moisture in a PCB is that it reduces the quality of metallization, lamination, solder mask, and PCB manufacturing processes.Due to the influence of water, the limit of thermal stress is excessive with the decrease of vitrification transition temperature.Sometimes it can also cause a severe short circuit, causing water to enter, leading to ionic corrosion.Other common properties of moisture absorption in PCB assemblies include flame retardation or layering, increased (DF) dissipation factor and (DK) dielectric constant, thermal stress over plating through holes, and oxidation of copper.
Ways to reduce moisture in PCB fabrication:
Regardless of the simple and complex technology used in PCB manufacturing, many operations in PCB engineering require wet process and removal of residual moisture.The raw materials used in PCB fabrication need to be protected during the PCB assembly process during storage, handling and stress response.The following is a brief guide to implementing controls at each stage of PCB operation:
1.laminated
Lamination is the dewatering step in PCB fabrication because the cores and prepreg are stacked together, bonding the layers to the laminate.The main controlling factors in the laminating process are temperature, time spent and heating rate.Sometimes when dryness is low, measures are taken to reduce the vacuum to reduce the possibility of internal voids attracting moisture absorption.Therefore, the use of gloves when handling prepreg is a good way to control the moisture level.This reduces cross-contamination.Non-corrosive humidity indicator CARDS should be flexible to address humidity levels when needed.The laminate should have a short washing cycle and be effectively stored in a controlled environment, which helps prevent moisture bags from forming in the laminate.
2.After laminating process and PCB assembly
After drilling, photographic imaging and etching operations in PCB fabrication, the moisture absorption rate captured in the wet process is higher.Screen printing solidification and welding mask baking are treated steps to relieve entrainment moisture.By minimizing the retention time between steps and even being keen to manage storage conditions, this can be more effective in reducing water absorption levels.By ensuring that the PCB is sufficiently dry during the early stages of lamination, the board can help reduce post-lamination baking operations.In addition, high quality surface treatments are used to prevent cracks during the drilling process and to remove residual moisture by baking prior to the hot air solder leveling process.The baking time should be maintained by taking into account the level of determination of moisture content, the complexity of PCB fabrication, PCB surface treatment, and sufficient thickness required for the board.
Therefore, it is important to keep up-to-date on the effects of moisture in PCB fabrication to avoid failures, damage and short circuits on the PCB and increase rework costs.Now, researchers are about to introduce more advanced solutions that save time, energy and cost by using environmentally friendly PCB technology to control moisture elements at every step of PCB manufacturing.
