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The LED chip adhesive is mainly used to fix the components on the printed board. It is generally distributed by dispensing or stencil printing to maintain the position of the components on the printed circuit board (PCB), ensuring uploading on the assembly line. The components will not be lost during delivery. After affixing the components and placing them in an oven or reflow machine, heat and harden them. It is not the same as the so-called solder paste. Once it is hardened by heating, it will not melt after reheating, that is, the thermal hardening process of the patch glue is irreversible. The effect of using SMT adhesives varies depending on the heat curing conditions, the materials to be joined, the equipment used, and the operating environment. When using, choose the patch glue according to the production process.
After the patch is coated, the components are mounted and can be sent to the curing oven for curing. Curing is a key process in the patch-wave soldering process. In many cases, the patch is poorly cured or not fully cured ( Especially in the case of uneven components on the PCB, the most common), in the process of transport, welding, components will appear off. Different types of rubber are used, and their curing methods are also different. Two types of curing methods are commonly used. One is heat curing, and the other is light curing:
The heat-cured epoxy type patch glue is heat-cured, and the early heat-curing is carried out in an oven. Now, it is mostly cured in an infrared reflow furnace to realize continuous production. In the formal production before the furnace temperature should be adjusted first, to make the corresponding product temperature curing curve, curing curve is more attention is: different manufacturers, different batch number of glue curing curve will not be the same; even if the same kind of patch Glue, used in different products, because the board size, components are different, the set temperature will be different, which is often overlooked. This often happens:
When IC devices are soldered, all the pins are still on the pads after curing, but after wave soldering, the IC pins will shift or even leave the pads and cause soldering defects. Therefore, to ensure the welding quality, we must adhere to the temperature curve for each product, and we must do a good job.
A. Two Important Parameters for Epoxy Curing The thermal cure of epoxy adhesives is essentially the fact that the curing agent catalyzes the epoxy gene at high temperatures. Open loop chemical reaction. Therefore, there are two important parameters that should be noticed during the curing process: one is the initial heating rate; the other is the peak temperature. The heating rate determines the surface quality after curing, and the peak temperature determines the bonding strength after curing. These two parameters should be provided by the patch glue supplier, which is more meaningful than the supplier provides only the curing curve, it can make you have some understanding of the performance of the patch glue used.
The effect of bond temperature on bond strength is more important than the effect of time on bond strength. At a given cure temperature, the shear force increases slightly with the increase of cure time, but when the cure temperature increases, the same cure time However, the shear strength increases significantly, but pinholes and air bubbles sometimes appear at excessive heating rates. Therefore, in the production, firstly, the PCB light board with components must be placed in an infrared oven for curing, and after cooling, carefully observe the surface of the patch with air bubbles and pinholes. If any pinholes are found, they should be taken seriously. Analyze the reason and find out how to eliminate it. In the furnace temperature curing curve, these two factors should be combined to reverse adjustment to ensure a satisfactory temperature curve.
B. Curing Curve Test Method The curing curve test method and equipment used for the patch glue in the infrared reflow furnace is the same as that for the solder reflow soldering furnace infrared reflow soldering furnace. It is not described here. The heating rate and curing temperature curve can be designed according to the parameters provided by the supplier. In case of disputes, in addition to consultations with suppliers, it is also possible to conduct differential scanning thermal analysis (DSC) to the relevant testing department to identify adhesive properties. Text / Shenzhen LED base
We know that LED patches generally have two curing methods: 1, thermal curing; 2, light curing. Xiao Bian today to take everyone to understand what is the LED chip heat curing?