When choosing flux, it needs to be decided according to welding products, customer requirements and equipment, and it is not allowed to buy and use it blindly.
Considering the product grade and product characteristics, it is the first consideration when choosing flux. For high-grade products such as computer motherboards, boards and other computer peripheral products and other motherboards or high-precision products, high-grade no-clean flux is generally selected, and a few customers use cleaning flux for welding before cleaning, including solvent cleaning and water cleaning flux. ?
For this kind of high-grade products, no matter whether cleaning-free flux or cleaning flux is selected, the reliability after welding must be guaranteed first, because tin plating on the general flux is not a big problem when the plate is intact, and the existence of residue or residual ions is the biggest hidden danger of the product. We suggest that this kind of products should use advanced non-cleaning flux. This flux has moderate activity and less residue after welding, and the ionic residue can be controlled at about 65438 0.5 μ gnacl/cm2, which greatly enhances the reliability of products after welding. ?
If you are not very confident about the no-clean flux, you can also choose to clean the flux and clean it after welding, which is the most reliable one in electronic assembly at present; If you need to choose cleaning flux, in order to promote environmental protection, we suggest that customers choose water cleaning flux, which has good welding effect and is easy to clean after welding. The high reliability after cleaning makes customers feel more at ease. ?
It is best to choose low-solid cleaning-free flux for mid-range products, such as the motherboard of high-end telephones and CD players. If this flux is selected, the surface after welding will be smooth, with less residue, no halogen or less halogen, which can basically ensure the electrical performance after welding, and generally will not cause problems such as leakage or electrical signal interference. ?
Generally speaking, the plates of low-grade electronic products are poor, mostly single-sided bare copper plates or precoated plates. If you choose high-grade no-cleaning and no-residue flux, the welding effect may be poor, and in addition, it may cause whitening due to the destruction of the original coating of the plate. In this case, we suggest choosing active prednisone flux. Although there are many residues on the surface after welding, the effect and reliability of tin plating can be guaranteed. ?
At present, most customers choose non-cleaning flux when tinning the pins of components such as wires, transformers, coils and patch transformers. After the customer's request for cleaning-free, we recommend the rosin-containing flux without cleaning and residue. This flux has moderate activity, good tin plating effect, no residue after welding, and no re-corrosion of component pins. In addition, the solder joint is bright and smooth with good wettability, which can achieve ideal welding. " ?
In short, the choice of flux in combination with products is to fully understand the characteristics of their products, including the grade of products, the situation of circuit boards, and the situation of components and pins, and then choose the flux suitable for their products.
2. Choose flux according to customer's requirements. ? Most manufacturers will put forward customers' requirements when choosing flux, especially electronic product OEM or OEM OEM OEM. Their customers have more stringent requirements or evaluations in this regard. Some manufacturers can't meet the requirements or have some difficulties in their own production, but after outsourcing this product to a foundry, they put forward the same or higher requirements.
Common customer requirements include the following aspects:
(1) The solder joint is full of tin. This is the requirement of more than 90% guests. In order to fill solder joints with tin, a flux with proper activity and good wetting performance must be selected. ?
(2) There is no residue or whitening on the board surface. Faced with this requirement of customers, most manufacturers will choose no-clean flux. If it is really caused by plate problems, they can choose the method of cleaning after welding to solve it. ?
(3) The solder joint is bright. The solder joint of 63/37 tin bar welding is usually bright. If the tin content is low or the impurities exceed the standard, the solder joint is relatively not bright. General flux will not cause extinction effect on solder joints unless it is extinction flux; The solder joints of rosin-based flux are brighter than those of flux without rosin. If the components that make the solder joint bright are added to the flux, the solder joint will be brighter after welding. ?
(4) Wuxi weld bead, continuous welding or virtual welding, missing welding and other bad conditions. These conditions are typical defects in electronic welding, and general manufacturers will strictly detect and control them. Anyone who has studied quality management knows the slogan "Good products are made, not tested", which tells us that it is much more important to control the occurrence of defects in the welding process than to repair them after they are done well. In order to ensure good quality in production, it is very important to choose flux correctly, because we have analyzed above, and these defects may be related to flux. Therefore, choosing the flux with proper activity and good wettability combined with good technology is the basic factor to avoid these shortcomings. ?
(5) No bad electrical performance such as electric leakage. If customers have such requirements, try not to choose flux with strong activity or high halogen content. If the plate is in poor condition, such flux must be used, and we can solve it by cleaning. If the cleaning cost or environmental protection requirements are considered, it is also a good idea to choose water cleaning flux when the product and other conditions permit.
3. Choose flux according to equipment and process conditions. ? Equipment conditions determine welding process conditions, and welding process conditions are the key link in selecting flux. For a simple example, if rosin flux is used in the peak furnace of spraying, it may not be suitable, because higher solids may block the nozzle of the sprayer in a short time; If you choose a flux that is only suitable for spraying for foaming wave soldering, the foaming effect may not be so good. According to the equipment and process conditions, the choice of flux has the following aspects:
(1) manual tin furnace?
There are two cases of manual tin furnace welding: foaming and non-foaming, and manual spraying is rarely seen in mass production. When there is no foaming, the range of optional flux is wider; When there is a foaming process, the flux with better foaming effect should be selected. Whether it is manual or automatic welding, our standards for better foaming are the same. First, the bubbles should be as small as possible, not too big; Second: the foam size should be uniform; Third: the foaming time should be as long as possible. ?
Because there is no preheating process in the manual tin furnace, some rosin-free cleaning and residue-free fluxes are generally not recommended to customers, and the use of such fluxes may cause defects such as tin beads; If the customer insists on using this flux, we suggest to try it out before deciding.
(2) Foam wave soldering furnace
Foaming flux must be selected for foaming wave crest furnace. At present, except rosin flux, the foaming problem of non-cleaning, non-residue and non-cleaning low-residue flux has long been solved. As for the standard of foaming quality, it has been discussed above. ?
(3) Jet welding furnace
In addition to the flux with high rosin content, there are many kinds of flux to choose from in the peak spray furnace. It would be better if you can choose a rosin-free no-clean flux. At present, some non-cleaning fluxes can be foamed or sprayed, so there is no big problem in choosing this process. ?
(3) Double wave soldering furnace?
Double wave soldering furnace is mainly used to produce mixed patches and plug-in circuit boards. At this time, the soldering surface of the circuit board needs to pass through two peaks. The peak of the first wave is high (also called high wave or turbulent wave), and its main function is to weld the preliminary fixed components; The second wave peak is relatively flat (also called flat wave or rectified wave), mainly to shape the solder joint.
In this process, the common problem is that when the flux passes through the first wave peak, the activator or wetting agent in it has been fully decomposed, so when it passes through the second wave peak, the flux actually has no function, and then it is easy to have bad situations such as continuous welding and sharpening. In order to solve this situation, we suggest that customers use flux with slightly higher solid content, and the activator and wetting agent should be resistant to high temperature; At the same time, in order to solve this problem, flux manufacturers often add compound activators and wetting agents to the flux, so that the flux can withstand different temperature ranges and still play its role as a welding aid after the first wave of welding.