How to improve reflow soldering when founding PCB burst-4
(3) The reflow temperature selection is not suitable as the triggering factor of the blasting plate. 1 The evoked effect of the temperature on the blasting plate By analyzing the sufficient and necessary conditions of the blasting mode, it can be known that they are all functions of temperature. The amount of volatiles in the multilayer board and its expansion pressure increase with increasing reflow soldering temperature, while the adhesion between the browning layer and PP decreases with increasing temperature. Obviously, the sufficient and necessary conditions for the latent burst must be induced by the temperature factor. Optimizing the reflow soldering temperature profile based on a comprehensive analysis of specific product characteristics is effective in suppressing the occurrence of cracking. 2 How to optimize reflow soldering temperature according to product characteristics (a) CG Woychik, a US microelectronics packaging expert, states: “With the usual SnPb alloy, the maximum temperature that components and PCBs can withstand during reflow soldering is 240°C. When using SnAgCu (lead-free) alloys, JEDEC specifies a maximum temperature of 260 ° C. Increasing the temperature may compromise the integrity of the electronic package assembly. Especially for many laminated structural materials, it is easy to delaminate between layers, especially These are new materials that contain more moisture. The combination of moisture and temperature rise inside will cause extensive delamination of most commonly used laminates (HDI laminated multilayer PCB boards). (b) JSHwang, an American electronic assembly and soldering expert, also wrote in his book "Welding Materials and Processes in Electronic Assembly Manufacturing": "Considering that the melting temperature of existing lead-free materials is higher than that of SnPb eutectic materials. The melting point temperature (183 ° C), in order to minimize the reflow temperature, a suitable reflow soldering temperature distribution curve is particularly important. He also pointed out: according to current production conditions, such as existing SMT manufacturers And the infrastructure includes the temperature characteristics of components and PCBs, etc. The peak temperature of lead-free reflow soldering should be kept at 235 ° C. After comprehensive analysis, in the lead-free reflow soldering of HDI laminated multi-layer PCB board, when used When SnAgCu solder alloy is used, the peak temperature is recommended to be 235 ° C, and the maximum temperature should not exceed 245 ° C. Practice has shown that after this measure is taken, the suppression effect on the blasting plate is very obvious.
