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We often see some PCB boards will be used in the red glue process, so why do SMT parts of the foundry to use red glue process?
SMT red glue is a single component epoxy resin adhesive that cures quickly after storage at room temperature and heat, it allows low temperature curing, ultra-high-speed micro-minor coating can still be maintained without pulling, overflowing, collapsing stable shape, its ‘shear-thinning’ viscosity characteristics and low hygroscopicity, it is suitable for use in room temperature aperture printing SMT process, the dot shape is very easy to control, stable storage and has an excellent adhesive dot shape. Its ‘shear-thinning’ viscosity and low hygroscopicity make it suitable for use in room-temperature aperture printing SMT processes.
SMT red adhesive is evenly distributed with hardeners,pigments,solvents and other adhesives,mainly used to fix the components on the printed board.It is mainly used to fix the components on the printed board, and then put into the oven or reflow soldering machine for heating and hardening after pasting the components.It is not the same as the so-called solder paste, once heated to harden,and then heated again will not dissolve,that is to say, the heat hardening process is irreversible.The effect of SMT adhesive will vary depending on the heat curing conditions,the object to be connected,the equipment used,and the operating environment.When using SMT adhesive,it is necessary to choose the adhesive according to the production process.
SMT red glue
The role of SMT red glue
1.When wave soldering is used,in order to prevent the components from falling off when the board passes through the solder tank, red glue is used to fix the components on the board.
2.In the process of double-sided reflow soldering,in order to prevent the large devices on the side that has been soldered due to the melting of the solder by heat and fall off,the use of red glue.
3.It is used in the reflow soldering process and the pre-coating process to prevent the displacement and stand-off during mounting.
4.In addition,when the quantity of printed boards and components is changed,it is used to mark them with a piece of adhesive.
Red glue process piping
1.Printing pipeline:Stencil engraved holes according to the type of parts,the performance of the substrate to determine the thickness and the size and shape of the holes.The advantages are high speed and high efficiency.
2.Dispensing pipeline:Dispensing is the use of compressed air,the red glue through the special dispensing head to the substrate,the size of the glue point, how much,by the time,the diameter of the pressure tube and other parameters to control the dispensing machine has a flexible function.For different parts,we can use different dispensing head,set parameters to change,you can also change the shape and number of dots to achieve the effect,the advantage is convenient, flexible,stable.The advantage is convenient,flexible and stable.The disadvantage is easy to have pulling wire and air bubble.We can adjust the working parameters,speed,time,air pressure and temperature to minimise these disadvantages.
3.Needle turn pipeline:It is a special needle film,immersed in a shallow glue tray each needle has a glue point,when the glue point touches the substrate, it will be detached from the needle,the amount of glue can be varied by the shape of the needle and the diameter of the size of the change.
The amount of glue can be varied by the shape and diameter of the needle:
1.The higher the curing temperature and the longer the curing time,the stronger the adhesive strength.
2.Since the temperature of the glue will change with the size of the substrate parts and mounting position,we suggest to find out the most suitable hardening conditions.
3.Curing time:100℃*5 minutes,120℃*150 seconds or 150℃*60 seconds.
4.Red glue storage:can be stored at room temperature for 7 days,in less than 5 ℃ storage of more than 6 months,in 5 ~ 25 ℃ can be stored more than 30 days.
red glue pcb
SMT red glue common problems:
1.Insufficient thrust causes are:
Insufficient amount of glue.
The gel is not 100% cured.
PCB board or components are contaminated.
The gel itself is fragile, no strength.
2.Insufficient glue volume or leakage causes and countermeasures:
The printing stencil is not cleaned regularly. Should be cleaned with ethanol every 8 hours.
There are impurities in the gel.
Mesh board opening unreasonable, too small or dispensing pressure is too small, the design of the glue is not enough.
Air bubbles in the gel.
If the dispensing nozzle is clogged, clean the dispensing nozzle immediately.
If the preheating temperature of the dispensing nozzle is not enough, set the temperature of the dispensing nozzle to 38℃.
3.Stretching
Pulling refers to the phenomenon that the glue cannot be broken when dispensing, and the glue is connected in a filament in the moving direction of the dispensing head. There are more wire connections, and the adhesive covers the printed pads, which will lead to poor soldering. This phenomenon is especially likely to occur when using a dispensing nozzle for larger sizes. The pulling of the adhesive is mainly affected by the pulling properties of the resin, which is the main component of the adhesive, and the setting of the dispensing conditions.
The solution to the problem of red glue:
1.Reduce the moving speed
2.The lower the viscosity and the higher the thixotropy of the material,the lower the tendency to pull the wire,so choose this type of glue as much as possible.
3.Adjust the temperature of the thermostat a little higher,forcibly adjusted to low viscosity, high thixotropy of the splicing glue,and then also take into account the storage period of the splicing glue and the pressure of the dispensing head.
The above is the red glue in the SMT parts of common problems and solutions, explains the SMT parts of the foundry why the red glue process?