The main contents of PCB solder paste incoming inspection are metal percentage, solder ball, viscosity, metal powder oxide content and so on. So what materials are tested in the PCBA assembly process? Next, share the PCBA assembly process materials.
(1) Percentage of metal. In the application of pcb, the percentage of metal in the solder paste is usually required to be 85% to 92%. The commonly used detection methods are as follows.
1 Take 0.1 g of the solder paste sample and put it into the crucible.
2 Heat the crucible and solder paste.
3 Curing the metal and removing the flux residue.
4 Weighing metal weight: metal percentage = metal weight solder paste weight × 100%.
(2) Solder balls. Commonly used solder ball detection methods are as follows.
1 A solder paste pattern having a diameter of 12.7 mm and a thickness of 0.2 mm was applied to the center of the alumina ceramic or PCB substrate.
2 The sample is dried and reflowed according to actual assembly conditions.
3 Check the solder after curing.
(3) Viscosity. The typical viscosity of solder paste used in SMT is 200~800Pa•s. The main factors affecting it are flux, metal percentage, metal powder particle shape and temperature. Rotary viscosity is generally used to measure the viscosity of the solder paste. The measurement method can be seen in the description of the relevant test equipment.
(4) Metal powder oxide content. Oxidation of metal powder is a major factor in the formation of solder balls. Auger analysis is used to quantitatively detect metal oxide oxide content, but it is expensive and time consuming. Qualitative testing and analysis of metal powder oxide content is often performed using the following methods.
1 Weigh 10 g of solder paste in a crucible filled with a sufficient amount of peanut oil.
2 heating in a 210 ° C heating furnace and reflowing the solder paste, during which the peanut oil extracts the flux from the solder paste, so that the flux cannot clean the oxide from the metal powder, and also prevents the metal powder during heating and reflow. Additional oxidation.
3 Remove the crucible from the furnace and add the appropriate solvent to dissolve the remaining oil and flux.
4 Remove the solder from the crucible and visually find the oxide layer on the metal surface and the degree of oxidation.
5 Estimate the proportion of the oxide coating layer, ideally an oxide-free coating layer, generally requiring no more than 25% oxide coating.