How to improve reflow soldering when founding PCB burst-5
(4) The loss of volatile substances is a contributing factor to the explosion
From the slice analysis, the location of the blasting plate occurs almost at the part of the buried hole covered with a large area of copper foil,
The manufacturability of this design is indeed problematic, mainly in the following aspects:
(1) After the welding is heated, it is unfavorable for the discharge of the volatility (such as moisture) accumulated in the buried hole and the interlayer;
(2) Intensifying the imbalance of the temperature distribution of the plate surface during reflow soldering;
(3) It is not conducive to eliminating the thermal stress during the welding process, and it is easy to form stress concentration, which aggravates the separation between the inner layers of the HDI laminated multilayer PCB.
Obviously, the graphic design of HDI laminated multi-layer board products is unreasonable, which promotes the occurrence of the explosion phenomenon in the lead-free process.
1.3 Mechanism of Explosion Occurrence (1) Mechanism of Explosion Plate According to the above analysis and induction of the characteristics of the explosion plate, we can study and analyze the physical process of the explosion plate according to the following physical mode. 1 The adhesion between the multilayer boards L1-L2 is good when the working environment temperature is not too high
As the heating and heating process progresses, the buried holes and the inner layer of volatile matter (including moisture) are continuously discharged.
3 The discharged volatile gas is concentrated between the buried hole and the PP (bonding sheet)
4 As the temperature continues to rise, the gas accumulated in the vicinity of the buried hole is more and more, forming a large expansion pressure, so that the browning surface of L2 and the PP are subjected to a separation force for separating them.When the final expansion pressure (f) is less than the adsorption force (F) between the browning surface and the PP (f<F), only a small bubble is left in the inner layer buried hole, that is, a dot-like shape is formed. Burst phenomenon6 When the final expansion pressure (f) is greater than the adsorption force (F) between the browning surface and PP (f>F), separation occurs between the browning surface of L2 and PP. A distinct blocky blistering phenomenon.
