LED SMT adhesive to cure
 
   
    SMT adhesive is mainly used to fix components on the PCB, usually plastic or steel with the point of printing methods to the distribution network in order to maintain components in printed circuit board (PCB) on the location, to ensure that the process of assembly line transmission components will be lost. After the paste components into the oven or re-flow of welding heat hardening. It is the so-called paste is not the same, one hardened by heating, after reheating will not melt, that is, SMT adhesive thermal hardening process is not reversible. SMT SMT adhesive effect of a result of the use of heat curing conditions, are connected objects, the equipment used, operating environments differ. When used according to production process to select the mount adhesives.
     SMT adhesive coating, the paste Zhuangwan components, can be sent to curing oven curing, curing adhesive is a chip - a key process in the wave soldering process, in many cases due to bad or incomplete curing SMT adhesive curing ( PCB, components, in particular the case of uneven distribution of health is most prevalent), during transport, the welding process, there will be parts fall off. Different types of plastic used in their curing methods are also different, two methods commonly used curing, a hot-curing, another is a light-cured:
1, heat-curing
     Epoxy adhesive patch thermal curing, the early heat-curing is carried out on the oven, and now is being focused on infrared reflow oven curing, in order to achieve continuous production. The formal pre-production should first adjust oven temperature to make the furnace temperature cure curves of the product, do pay more attention to curing curves are: different manufacturers, different batches of SMT adhesive curing curve will not be the same; even if the same kinds of paste plastic film used in different products, because of board size, the number of different components, the set temperature will be different, which is often overlooked. Will often be the case: In the IC device during soldering, curing, all of the pins also falls on the pad, but after wave shift occurs after the IC pins or even to leave the pad and produce welding defects. Therefore, to ensure the welding quality, should insist on the temperature curve of each product have to be done, but also to do a good job.
A. epoxy adhesive curing two important parameters
     The heat-curing epoxy adhesive patch, and its essence is the high temperature catalytic curing agent in epoxy gene. Ring-opening reaction occurs. Therefore, the curing process, there are two important parameters on the attention should be given: First, initial heating rate; second peak temperature. Heating rate-determining surface quality after curing, while the peak temperature determines the bonding strength after curing. The two last parameters should be SMT adhesive suppliers, more than suppliers only provide a more meaningful cure curves, which enables you to mount adhesives used in an understanding of the performance. Figure 26 is used at different temperature curing adhesive cure curves of a patch.
    Bonding temperature on bond strength of impact than the impact of time on the bond strength is more important at a given curing temperature, curing time with the increase in shear force small increase, but when the curing temperature increases, the same curing time Village shear strength was significantly increased, but the fast heating rate is sometimes occur pinhole and bubble. Therefore, in production, should first hold onto components with the PCB Bare Board, after dispensing into the infrared oven curing, cooling, after careful observation with a magnifying glass surface mount adhesives have bubbles and pinholes, if it pinhole should be carefully analyze the reasons and find the removal method. Temperature curing curves do, we should combine these two factors repeated adjustments in order to ensure that get a satisfactory temperature curve.
Cure curves of the test method B.
     SMT Glue in infrared reflow oven curing curve of test methods and the instruments with infrared solder paste reflow furnace temperature curve of the same way, this is no longer introduced. The heating rate and curing oven temperature curve according to the design parameters provided by the supplier. In addition, when the controversial encounter in consultation with the supplier, but also can go to the testing department differential scanning thermal analysis (DSC), identification of adhesive performance.
2, light-curing
     When using light-curing adhesive, then the use of UV light with a reflow furnace to cure, the curing is fast and high-quality products. Reflow furnace is usually attached to lamp power addition, 2-3kW, from the PCA is about 10cm high by 10-15s on the so exposed to the elements in vitro rapid-curing adhesive patch, while the furnace temperature of about 150-140 ℃ maintained 1min , we can make the following adhesive curing components thoroughly.
     The use of needle-less transfer method 10% of all applications, it is the use of needles arranged array immersed in a tray adhesive. Then gum drops suspension transferred to the board as a whole. These systems require a lower viscosity of the adhesive, but also has good resistance to moisture absorption, because it exposed in the indoor environment. Control the needle key factors include the transfer of Epoxy needle diameter and style, glue temperature, immersion depth and Epoxy needle cycle length (including needles and PCB exposure before and during the delay time). Pool tank temperature should be between 25 ~ 30 ° C, which controls the viscosity and adhesive glue on the number and form.
     Templates are widely used in solder paste printing, and distribution of adhesive can also be used. Although less than 2% of the SMA model is printed, but this approach has increased interest in the new equipment is to overcome some of the earlier limitations. The correct template parameter is the key to achieve good results. For example, contact printing (zero away from the plate height) may require a delay period to allow the formation of a good gel-point. In addition, the model of polymer non-contact printing (approximately 1mm gap) requires the best squeegee speed and pressure. Metal template thickness of 0.15 ~ 2.00mm, should be slightly larger than (+0.05 mm) gap between the components and PCB.
     Finally the temperature will affect the viscosity and the gel-point shapes, most modern Epoxy machine needles lips or capacity to rely on room temperature control device to keep the temperature above room temperature glue. However, if the PCB temperature from the previous process was improved, then the gel-point profile may be damaged.