PCB manufacturing companies clean - free flux requirements

In order to make the soldered PCB meet the specified quality requirements without cleaning, the selection of flux is the key. PCB manufacturing companies usually have the following requirements for the solders without cleaning

1.Low solid content, conventional solders have high solid content (20%-40%), medium solid content (10%-15%) or low solid content (5%-10%). PCB surface after welding with these solders has more or less residue, while the solid content of no-cleaning agent is less than 2% and does not contain rosin. Therefore, there is basically no residue on the welded surface

2. Non-corrosive.Traditional flux with high solid content, after the welding part harmful substances can be "wrapped" , isolation from the solder joint contact with air, form the insulating layer, and no clean flux cannot form the insulating layer due to the extremely low solid content, if there is a small amount of the harmful ingredients of residue on the surface, will cause serious consequences such as corrosion and leakage.Therefore, halogen components are not allowed in PCB manufacturing companies' no-cleaning flux. Corrosion of flux is usually tested in the following ways.

(1) Copper mirror corrosion test: test flux (solder paste) short-term corrosion.

(2) Silver chromate test paper: test the content of halide in flux

(3) Surface insulation resistance test, test the surface insulation resistance of PCB after welding, to determine the reliability of the long-term electrical performance of flux (solder paste)

(4) Corrosion test: test the corrosion of residue on the surface of PCB after welding.

(5) Test the degree of reduction of component spacing on PCB surface after welding

3. Weldability.In order to make the flux has a certain ability to remove oxide, and in the whole process of preheating and welding can maintain a certain level of activity, it must contain certain acids, in no clean flux, with the most is a water soluble acetic acid series, formula may contain amine and ammonia and synthetic resin, different formula will affect its activity and reliability.Different PCB manufacturing companies have different requirements and internal control indicators, but must meet the requirements of high welding quality and non-corrosive