Voiding is a common problem when soldering with lead-free solder paste
. Spacing between grains of lead-free solder paste can also cause voids. In addition, due to the inconsistent diffusion rate of metal elements, vacancies are usually left in the intermetallic compound body, and the vacancies will form cavities after continuous accumulation. The presence of voids results in compromised electrical and thermal properties. Solder joints, on the other hand, show significant void growth after thermal aging and can lead to failure. So how do you quantify the impact of voiding on solder joint performance? Next, the solder paste manufacturer will explain to you:
The melting point of LFP-0M-305 lead-free solder paste is about 217°C, so it is considered to be a more suitable connection material for flip-chip LEDs. Use LFP-0M-305 lead-free solder paste to complete the DA3547 LED chip package. Many people have discussed how the volume of solder paste can directly affect the generation of voids in LED chip packaging, and the adverse effects of void rate on thermal and mechanical properties.
1. The adverse effect of lead-free solder paste volume on voids
Using X-ray observation, it is reflected that the moderate increase in the volume of the lead-free solder paste effectively greatly reduces the void rate in the solder paste body. After calculation, the void ratios of LED chip samples a and b are 46% and 3%, respectively. Too little lead-free solder paste will cause too much spacing between the particles, which will easily accumulate into voids after soldering. So that appropriately improving the amount of tin also has a certain effect on greatly reducing the void rate.
2. The adverse effect of voids on LED chip packaging
The shear strength of LED chip packaging has a close relationship with the void ratio. Voiding in large volumes can also cause a significant reduction in reasonably effective weld capacity, or increase internal pressure. The greatly reduced effective area implies that the pressure will also be more intensive, resulting in a greatly reduced wear resistance or an increased possibility of fracture phenomena. When the void rate is 46%, the shear strength of the LED chip is only about half of that of the chip with a void rate of 3%. A large void rate will also increase the temperature of the LED chip. Many people also found that the LED chip temperature for large void ratio is 40.5°C. The working environment temperature of LED chip with small void ratio is only 36.9°C. It can be seen that increased voiding also has adverse consequences on the conductivity of the chip. The reason is that the heat caused by the void rate is too dense, and the solder cannot effectively and effectively volatilize the heat, so as to cause high temperature resistance.
Many people use the calculated thermal conductivity to know that when the void rate of the LED chip package is too much, the thermal conductivity of each layer is generally a bit too large. It must be measured in the PI layer and TIM layer that the thermal conductivity of the chip with small holes is significantly greater than that of chips with large holes. On the whole, chips with a small void rate have better thermal performance.