Flux Key technology Q&A

1. There is no uniform standard to distinguish no-clean flux from non-clean flux.

First clarify a concept about cleaning and non-cleaning, even if the so-called no-cleaning flux, it cannot be said that it does not need to be cleaned or can not be cleaned, and the so-called non-no-cleaning flux does not mean that it must be cleaned after welding.

Some people say that the difference is based on whether it contains rosin or not or how much rosin it contains, but it is actually incorrect. Even if the rosin is slightly more, but the coating after welding is more uniform, the guest does not need to clean, it can also be called no-clean flux, if the rosin is very little, but the guest is cleaned after welding to ensure safety, then at this time, it is non-no-clean flux.

The flux can not be divided into no-cleaning or non-no-cleaning type, in fact, whether it needs to be cleaned is not the flux manufacturer, but whether the user needs to clean, the manufacturer often said that no-cleaning flux, in fact, is not the correct statement, can only be said that the flux can not be cleaned, referring to my 2005 published in the "tin solder" article, the flux is classified as follows:

(1), rose-scented flux

This kind of flux is the traditional type of flux, relatively speaking contains more rosin or resin, so the solid content is high, more than 15~20% or more, the general rosin flux contains a small amount of halogen, so the weldability is strong, can be applied to a variety of plates, the welding surface after welding will have a layer of extremely thin protective film, so as to protect the solder joint from oxidation, not by moisture erosion.

Rosin flux development to the mid-1990s, there are many customers using rosin flux, began to notice the residual problem after welding, in order to achieve a better smooth effect, many customers took the method of cleaning after welding, which many experts believe that this "with rosin flux welding, welding and then cleaning process" is currently the most reliable welding method. However, the increase in the post-welding cleaning process caused the rise in production costs, and soon became a problem that plagued customers, therefore, a new type of rosin flux came into being, this flux also contains rosin, but the rosin content is not very much, and can not be cleaned after welding, which is what we want to talk about in the following "no-clean low solid flux".

Combined with the above, we can find that in fact, in the rosin flux, it can be roughly divided into "rosin non-cleaning type, rosin cleaning type and rosin no-cleaning type" three kinds.

(2) No-clean low solid flux

This kind of flux is directly evolved from the rose-scented flux, it acts as a transition from "rose-scented flux" to "no-clean no residue flux" development process; They contain rosin or resin, but the content is not much, the general solid content is 8~10% or less, most of them contain a small amount of halogen and some do not contain halogen, halogen content basic requirements are controlled below 0.2%, the welding performance can basically achieve the effect of ordinary rosin, but the welding surface is relatively clean, can be cleaned or not cleaned; Relatively speaking, the "weldability" and "reliability" of this kind of flux are stronger than that of "no cleaning no residue flux", and slightly weaker than the rose-scented flux, but the reliability after welding can generally meet the requirements of customers.

(3), no cleaning no residual flux

No cleaning no residue flux from the middle of the last century began to be gradually promoted in China, in the early promotion because of various technical defects, and accustomed to the use of rose-scented flux customer rejection, until the 1990s gradually accepted by the market, at the same time our country developed a no-cleaning flux related industry standards.

After 2000, more and more customers use a variety of no-clean flux, while customers put forward higher requirements for no-clean flux, from the appearance of the requirement of "colorless and transparent" to the weldability of the flux itself, as well as the surface residue and ion residue after welding are more and more stringent.
Although the above two types of flux are called "no-clean" flux, we usually need to understand that the "no-clean" flux is not can not be cleaned, nor is it completely unnecessary to clean, not completely without post-welding residue, similar to the "no-clean no residue" type of flux, but relatively speaking, the residue is less. Here to understand is actually "no cleaning" and "no residue" such two concepts, whether the need for "no cleaning" and whether to clean, depends on the requirements of the welded product itself, in the precision electronic assembly process, or require 100% quality assurance, such as military, aerospace or medical electronic products assembly process, any extremely trace residues are possible Lead to poor products, therefore, most of the time these industries can not do the real "free cleaning"; Only in specific cases, under specific conditions, when the residue of the flux is not enough to cause bad products, it is possible to achieve real "no-cleaning".

2. What is the difference between the formulation of the matting flux and the non-matting flux? Is the effect just a difference in the solder joint brightness? Will it have different effects on other aspects of welding?

Regarding the addition of brightener and matting agent in the flux, if the two kinds of flux are directly compared, of course, the effect exists only in the difference between whether the solder joint is bright.

As for whether it will have different effects on welding in other aspects, it is impossible, but generally speaking, it is not too much, because the main role of this additive is the solder joint bright or dull, of course, many raw materials have a variety of functions at the same time is normal, for example, some brightener also has a certain chemical activity, can help remove the oxide layer, improve the welding speed and other conditions The.

In general, if the correct matting agent or brightener is selected, there will be no impact on the quality of welding.

3. Does the washless flux affect the long-term reliability of welding quality (such as corrosion of PCB), and how corrosive is the welding equipment

In the current no-cleaning residue-free flux, there are two categories containing rosin (resin) and no rosin (resin), the solid content of these two types of flux can be guaranteed at about 2% or less, so the residual surface after welding can meet customer requirements; At the same time, because there is no rosin or less rosin content, most flux manufacturers in order to enhance the solderability of the flux, from the addition of more activators and wetting agents to improve the solderability of the flux, which is also a reason that many customers who are used to the rosin type of flux can not quickly accept, because they fear that in the absence of rosin, strengthening the activator will cause hidden dangers after welding. In fact, in the early days of the promotion of "no-cleaning no residue flux", such problems do exist, and with the continuous improvement and maturity of technology, this situation has been well solved so far. In terms of appearance, most of them can be colorless or lighter color and transparent, no precipitation and suspended matter, and can maintain the stability of physical properties.

In addition, most of this kind of flux does not contain halogen, which basically ensures that there is no ion residue or very little ion residue after welding. According to the relevant international standards such as J-STD-001B and MIL-STD-2000A, the ion contaminants after welding of no-clean flux should be below 1.56μgNaCl/ cm2. General reference is made to the classification of residual flux ion levels: the first level is below 200μgNaCl/cm2, the second level is below 100μgNaCl/cm2, and the third level is below 40μgNa-Cl/cm2; If the above requirements can be met, it can basically ensure that there is no leakage or subsequent corrosion of the welding surface, and ensure the stability and reliability of the welding.