Chemask® WF Solder Masking Agent: An Advancement in Water Removable Spot Masks
This article is based on an original publication by Chemtronics.
Modern circuit board manufacturing involves a number of automated steps designed to achieve the most efficient production process and highest quantity possible. This may involve a range of chemicals including soldering flux, adhesives, solder paste and temporary spot mask. Although necessary, these formulas may leave residues which can be detrimental to board performance.
One of the most efficient methods of residue removal is found through aqueous cleaning processes. An in-line, closed-loop aqueous system involves recirculating process water through deionizing resins, thereby removing contaminants and allowing the water to be reused. While water-soluble spot masks were designed to increase efficiency and throughput, some contain materials that could result in reduced process life of deionizing resins, causing more frequent replacement of resin beds and increased manufacturing costs.
In light of this issue, Chemtronics® offers Chemask WF Solder Masking Agent, a temporary water filterable mask that can be easily removed using aqueous cleaning systems without affecting deionizing resin beds.
Circuit Board Assembly
Generally circuit board assembly can be broken down into three phases: component placement, soldering, and aqueous cleaning. The initial two processes can expose the board to contaminants that could affect integrity of deionizing resin beds. Although boards are cleaned, they may still contain chemical traces when they reach the component placement phase.
Once in the assembly area, the PCB continues to meet with contamination as adhesives are screened onto the board and solder paste is applied. Following this process, a spot mask is used to protect contact surfaces onto which other components will be added - generally those with unconventional geometry or heat-sensitive pieces - before moving on to wave soldering. Flux is applied to ensure proper solder contact and the board is preheated, activating the flux in preparation of high molten solder temperatures. Once passing through the wave solder, through-hole components are bonded to the board. The circuit board cools and is now ready for aqueous cleaning.
A necessary component of contamination removal as well as removal of solder flux and paste residue, aqueous methods are the preferred way to clean circuit boards due to cost and environmental considerations.
In both open- and closed-loop aqueous cleaning, water is first deionized as it is pumped into the system. While an open-loop aqueous cleaning system sends rinse water to waste treatment, in closed-loop cleaning the water is separated, filtered and recycled.