Every in the same way printed circuit board must be used in the processing of various types of chemical drugs, but not everyone understood chemical residues on the impact of electronic assembly production. Printed circuit board maker for surface cleaning of the important role of importance for subsequent Assembly of electronic products to produce a safe, reliable, stable and practical product is vital, in the electronics industry, ion chromatography analysis is an important tool. Using this method, can be qualitative and quantitative analysis of process residues, and point out its source. So, what are the chemical substances is useful for PCB production, but to the assembled and does the opposite?
Most people only know that chlorine sterilization, in tap water and swimming pool are often used. Chlorine bleach can also make our clothes so white and bright, but daily life and electronic products are not the same. PCB producers should be concerned about are the following things:
1. PCB assemblers, the presence of chloride ions can cause leakage, erosion and ionization of metallic substances. Chlorine is a Nonmetal activity is very strong material. Component on the Board if there is adequate chloride ion, and combine tidal water in the form of chloride ion-selective electrode potential, can cause corrosion and metal ionization.
2. in printed circuit manufacturing process, there are many potential sources of chloride ions. In normal circumstances, identify all sources of chloride ions is difficult. Often this occurs include: hot air leveling (HASL) flux, operator of sweat from the skin and the cleaning of tap water, and so on.
3. the chlorine ion content aided welding flux chemical composition influence. Due to the natural properties of rosin resin, Assembly process using solid high quality Rosin soldering flux (such as activating fluxes or mildly active flux), relatively high levels of chloride ions. Resin based or water-soluble Rosin-based flux and non-cleaning flux in this regard is the opposite. Ultimately, therefore, for assembling welding process of water-soluble lower or no clean flux of chloride ion content.
4. the chlorine ion content under the influence of material of PCB Board. Material of PCB Board (including its insulating substrate and attached metal) determines the permissible chloride content in the Assembly process. Ceramic mixture substrate formation of refractory material or other materials, such as aluminum, epoxy glass cloth substrate organic substrates such as more sensitive to the presence of chloride ions. This is partly due to integrated distribution has reached the surface micro-scope level. As far as the metal layer on the surface, NI/au surface itself is much cleaner than the lead/Tin surface.
In contrast, bromide for stability of circuits smaller than chlorine. Bromine use is as a flame retardant in epoxy glass cloth to add material. PCB manufacturing process of bromide in places including solder, character ink and some bromide-activated flux of materials. Corrosion effects of bromo-mainly from the flux residues (for example, HASL flux). Bromine content, degree of loose sheet metal or solder voids-related, so wood boards or solder how to, reflecting the level of bromine. In addition, the high temperature cleaning of the Board also works for bromine, bromide size of the impact and process of printed circuit boards, in particular mount weld before the hot air leveling land related to the washing machine.
Third, the sulfate ion
With chlorine, bromide ion has the same effect as more than the presence of sulfate, also can cause damage to the electronic Assembly materials. Sulfate from many PCB processing technology, including a variety of kraft paper, plastic material and used in the micro-etching acid, and so on. Most often, sulfate ion from the rinse or wash with running water.
Four, methyl sulfonic acid
Methanesulfonic acid (MSA) is a caustic chemical, normally used in the electroplating process for many. We have now found that MSA is also used in some hot air leveling flux was as a substitute for the active agent. If the MSA is not fully neutralize or clean, the corrosive effect of chlorine would be many times higher. MSA chemical equilibrium equations are as follows:
CH3SO3H(aq) ------ CH3+(aq.)+HSO3- ------- (aq.)
Where: formaldehyde CH3+=
HSO3-= hydrogen sulfide or sulfonates (anion)
Five General principles, clean
How is clean enough? Determine the answer now seems to be: "not sure". Traditionally, most of the surface cleanliness of military standards and business standards are marked only "acceptable" and "unacceptable" limits. But such arguments generally do not take into account the complexity of the Assembly components, end user environment or reliability, and so on. Most industry standards attach to the fact that, namely, surface cleaning standards must be based on a series of already or potential adverse effects on the assembled products issues. Therefore, in the present case, it is unable to provide a unified, complete, precise standards for cleanliness of finished printed circuit board layout.
United States pollution research laboratory (CSL) according to the Decade in solving practical problems and accident analysis data of experience, has provided a number of relevant specifications for surface cleanliness.