How to improve reflow soldering when founding PCB burst-6
While the PCB is heated, part of the free volume of water can be dissipated through the microporous PCB substrate, thereby reducing the molar volume fraction of water that may accumulate at the voids or microcracks, which is beneficial to the explosion of the PCB. improve. However, if the surface of the PCB has a large area of copper foil pattern coverage, when the PCB is heated, the large copper foil surface above the buried hole blocks the water vapor that escapes outward after being heated, so that the pressure of water vapor in the microcrack increases, resulting in occurrence of The chance of a burst is greatly increased.
1.4 Countermeasures for pre-explosion plates
(1) The necessary conditions for eradicating the occurrence of a blasting plate
· The biggest problem in PP storage is to prevent it from absorbing moisture, and the moisture in the air is easily condensed on the PP to become adsorbed water. In order to maintain the original performance of the PP, the suitable storage conditions are: temperature (10 ~ 20) ° C, humidity < 50% RH (preferably stored in vacuum). It has been reported that storage of sheets at 5 ° C for one month or longer does not successfully produce high quality multilayer boards, so refrigeration is also undesirable.
· Strictly control the storage conditions of PCB finished products, especially in rainy weather, increase the power of the dehumidifier to control the humidity of the warehouse;
· Improved packaging for lead-free process PCB products, vacuum film + aluminum film packaging to ensure storage time and dryness; · Find new materials with good heat resistance and low moisture absorption.
(2) Sufficient conditions to suppress the occurrence of blasting plate · Optimize the quality of “browning” process and increase the adhesion between layers inside PCB; · Select high-quality browning syrup; · Strengthen the monitoring of raw material quality, such as resin content of PP material (RC%) ), resin gel time (GT), resin fluidity (RF%), volatile matter content (VC%) and other key indicators. In order to ensure the uniformity and occupancy of the resin present in the impregnated fiber space, it is ensured that the finally formed substrate material has low water absorption, better dielectric properties, good interlayer adhesion and dimensional stability.
(3) Gas permeability of the Shanshan copper foil surface According to the above-mentioned positional characteristics of the explosion plate and the mechanism of the occurrence of the explosion. Obviously, when the surface of the PCB has a large area of copper foil layer design, the internal water vapor will not be released, so it is necessary to open a window to the area with a large copper surface on the surface to improve the explosion phenomenon.
(4) Optimizing the peak temperature of reflow soldering To ensure good wetting, the peak temperature of reflow is appropriately reduced.
