LED patch glue and Dijiao basic knowledge

- Apr 06, 2017-

1, the role of patch adhesive surface adhesive adhesive (SMA, surface mount adhesives) for the 

wave soldering and reflow soldering, mainly used to components on the printed circuit board, the 

general use of dispensing or stencil printing method to allocate To maintain the position of the 

component on the printed circuit board (PCB), ensuring that the components are not lost during 

transmission on the assembly line. Paste the components into the oven or reflow machine heating 

hardening. It is not the same with the so-called solder paste, once heated and hardened, and then 

heating will not melt, that is, the film heat hardening process is irreversible. The effect of the 

SMT patch will vary depending on the heat curing conditions, the connectors, the equipment used, 

and the operating environment. When used in accordance with the production process to choose patch 

glue.


2, the composition of patch adhesive PCB assembly used in most of the surface patch adhesive (SMA) 

are epoxy (epoxies), although there are polypropylene (acrylics) for special purposes. In the 

introduction of high-speed Dijiao system and the electronics industry to master how to deal with 

relatively short shelf life of the product, the epoxy resin has become the world's more mainstream 

glue technology. Epoxy resins generally provide good adhesion to a wide range of circuit boards 

and have very good electrical properties. The main ingredients are: base material (ie, the main 

polymer material), filler, curing agent, and other additives.


3, the use of patch glue purpose a. Wave soldering to prevent component off (wave soldering process)

b. Reflow to prevent the other side of the components off (double-sided reflow process) c. To prevent

component displacement and legislation (Reflow process, pre-coating process) d. For marking (wave 

soldering, reflow soldering, pre-coating), printed circuit boards and components to change the 

volume, with patch adhesive for marking.


4, the use of patch glue classification a. Dispensing type: through the dispensing equipment in 

the printed circuit board sizing. B. Scraping type: sizing by stencil or copper screen printing.


5, Dijiao method SMA can be used syringe Dijiao, needle transfer method or template printing method

applied to the PCB. The use of the needle transfer method is less than 10% of the total application,

and it is used in the tray of the gel in the array of needles. And then hang the droplets as a whole

to the plate. These systems require a lower sticky glue and have a good resistance to moisture 

absorption because it is exposed to the indoor environment. Key factors that control needle transfer

dipping include needle diameter and pattern, the temperature of the gel, the depth of the needle im-

mersion, and the length of the duration of the dispenser (including the delay time before and during

contact of the needle). The tank temperature should be between 25 and 30 ° C, which controls the 

viscosity and the number and form of glue.


Template printing is widely used in solder paste, also available with the distribution of glue. 

Although less than 2% of SMA is currently printed with templates, interest in this approach has 

increased and new equipment is overcoming some of the earlier limitations. The correct template 

parameter is the key to achieving good results. For example, contact printing (zero plate height) 

may require a delay period, allowing good glue to form. In addition, non-contact printing (approxim

ately 1 mm gap) for polymer templates requires optimum scraper speed and pressure. The thickness of

the metal template is generally 0.15 to 2.00 mm and should be slightly larger than the (+0.05 mm) 

gap between the component and the PCB.

The final temperature will affect the viscosity and the shape of the dot, and most modern dispensers

rely on the temperature control device on the mouth of the mouth or the chamber to keep the gel temp

erature higher than room temperature. However, if the PCB temperature from the front of the process

to improve, then the plastic dot contour may be damaged.


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