Right from the Material melds, PCB design, prototyping, PCB engineering, assembling to packaging and order delivery stage, the effect of moisture in PCB fabrication should be taken care of to avoid damages and other issues in the functioning of the PCB. Furthermore, let’s take a dip into significant measures implemented for controlling the humidity level during the process of lamination, at the time of PCB assembly and controls implemented during storage, packaging and shipping of order.
How moisture can create a great fuss in printed circuit boards?
The moisture can forge ahead various defects in the PCB assembly by its presence in epoxy glass prepreg, diffused in PCB during storage process, absorption at the time of wet processes in PCB manufacturing, residing in the micro cracks or can make a home in resin interface. As the high temperature and vapor pressure go parallel with led-free mechanism in PCB assembly, it results in uptake of moisture level.
Along with the adhesive and cohesive malfunctions in printed circuit boards resulting in Delamination or Cracking, moisture can make the metal migration possible that can cause low impedance path with variation in dimensional stability. With more technical damages like reduction in glass transition aridity, rise in dielectric constant and many more, it results in lower speed of circuit switching and high level of delay in propagation times.
The major effect of moisture in PCB is, it reduces the degree of quality of metallization, lamination, solder mask and the process of PCB manufacturing at large. The limit of thermal stress goes in excess with the reduction of glass transition temperature due to the effect of moisture. Sometimes it also leads to critical short circuits with the effect of moisture ingress that results in ionic corrosion. The other common attributes to moisture absorption in the printed circuit board assembly includes Blisting or Delamination, increases the (DF) dissipation factor and (DK) dielectric constant, thermal stress on plated through hole and oxidization of copper.
Ways to mitigate moisture in PCB fabrication:
Whether the PCB fabrication uses simple or complex technologies, there are many operations in PCB engineering that requires a wet process and also removal of residual moisture. The raw materials used in PCB manufacturing need protection during storage, handling and tackling stress during PCB assembly process. A short guide to controls implemented at the time of various stages of PCB operation is addressed below:
Lamination is a dehydrating step in PCB fabrication as the cores and prepregs are stacked with bonding the layers into the laminate. The chief elements to control in the process of lamination is the degree of temperature, time taken and heating rates. Sometimes with low aridity, the steps are taken to decrease the magnitude of vacuum to lessen the chance of internal voids that attracts the humidity to get absorbed.
2. Post lamination processes and PCB assembly
After the drilling, photo imaging and etching operations in PCB fabrication, the moisture absorption rate is higher as it gets entrapped during the wet processes. The silkscreen cure and solder mask bake are steps that are processed to get relief from the entrapped humidity. This adds up to more effective in reducing the level of moisture uptake by minimizing the holding time interval between the steps and even keen in managing the storage conditions. By ensuring at the early stage of PCB lamination that circuit boards are sufficiently dry can help reduce baking operations after lamination. Also, using a high quality surface treatment to prevent cracks during drilling and removing the residue humidity by baking before the process of hot air solder levelling. The baking time should be kept by considering the decided level of moisture content, complexities in the PCB fabrication, PCB finish and adequate thickness required in the circuit board.
Thus, it is vital to get updated on the effect of moisture in PCB fabrication to avoid malfunction, damages and short circuit on the PCB with increasing the cost of rework as well. Researches are now upcoming with more advanced solution to control the element of moisture in each and every step in PCB manufacturing that saves time, energy and cost by using environmentally friendly PCB technologies.
MOKO has a combined and extensive years of experience in PCB engineering, prototyping, PCB designing, assembly process and PCB fabrication. Having a strong customer base from different sectors, they have a well defined Fabrication Unit with the high tech tooling room. Our team of skilled engineers have experience in tackling and providing an optimum solution to any king of printed circuit board project. To know more about our PCB services and projects, visit http://www.mokopcb.com/