PCBA Tech - What is the viscosity value of SMT red glue

What is the viscosity value of SMT red glue

The viscosity of patch red glue is mainly affected by three factors, namely temperature, pressure and time. The specific reasons are as follows:
1. The viscosity of patch red glue is affected by temperature
The viscosity of the patch red glue is greatly affected by temperature. According to the test data of Dongguan Hisilicon Electronics Co., Ltd. in the middle of multiple tests, it is shown that when the test temperature increases by 7°C, the viscosity of the patch red glue drops by 40%. When the viscosity drops during production, it means that the amount of red glue dotted by the needle tube increases, while the height of the glue dots on the PCB circuit board drops, so the temperature of the red glue should be constant during dispensing, generally kept at Around 25 degree Celsius to ensure the ideal red glue dot shape.

2. The viscosity of patch red glue is affected by pressure

The viscosity of the patch red glue is affected by pressure. In the pressure-dispensing coating process, as the pressure increases, the faster the red glue will come out of the emulator, that is to say, the cutting The cutting speed is increased. Generally, the pressure of the dispenser is controlled within 5bar (1bar=1kPa) in production, and it is generally set at a center value of 3.0-3.5bar. The high pressure will increase the cutting speed and make the needle tube head Fever, causing deterioration of the red glue function of the patch.

3. The viscosity of patch red glue is affected by time

The viscosity of the patch red glue is also relatively affected by time. The patch red glue has a little retention period. Assuming that the patch glue crosses the retention period, the viscosity will increase. This is an indirect effect of time on the viscosity of the patch red adhesive. But in the injection dispensing process, it can affect the amount of glue. As time increases, the amount of glue becomes larger.
(1) Since it is not a dispensing process but a printing process of red glue, there are certain requirements for the thixotropic index and viscosity of the red glue. If the thixotropic index and viscosity are not good, the shape after printing is not good, that is, the phenomenon of collapse. There may be some IC bodies that cannot be glued with red glue and are prepared. (Reference thixotropic index: 4-5; reference viscosity: (8-10) x1000000)
(2) The uncured glue stuck on the PCB circuit board can be wiped off with acetone or propylene glycol ether or cleaned with a special cleaning agent for red glue.
(3) Refrigerate the unopened products in a dry place at 2-10°C. The storage period is 6 months (subject to the date of delivery outside the package). Before use, return the product to room temperature and warm it up for more than 24 hours.
(4) Choose the curing time to be as short as 90-120 seconds, and the curing temperature is better to be around 150 degrees.
(5) It must have good heat resistance and excellent electrical properties, as well as extremely low moisture absorption and high stability.
Matters needing attention in parameter adjustment of smt patch red glue printing machine
(1) The pressure is about 4.5 kg
(2) The amount of red glue added should make the red glue roll on the template.
(3) The distance in SNAP OFF is set to 0.05mm, and the speed is set to: Level 2.
(4) The frequency of automatic screen cleaning is set to 2.
(5) After production, the red glue on the template is scrapped when it is no longer used within 5 days
(6) The red glue must be printed accurately between the two pads without offset. (1) Since it is not a dispensing process but a printing process of red glue, there are certain requirements for the thixotropic index and viscosity of the red glue. If the thixotropic index and viscosity are not good, the shape after printing is not good, that is, the phenomenon of collapse. There may be some IC bodies that cannot be glued with red glue and are prepared. (Reference thixotropy index: 4-5; reference viscosity: (8-10) x1000000)
(2) The uncured glue stuck on the circuit board can be wiped off with acetone or propylene glycol ether or cleaned with a special cleaning agent for red glue.
(3) Refrigerate the unopened products in a dry place at 2-10°C. The storage period is 6 months (subject to the date of delivery outside the package). Before use, return the product to room temperature and warm it up for more than 24 hours.
(4) Choose the curing time to be as short as 90-120 seconds, and the curing temperature is better to be around 150 degrees.
(5) It must have good heat resistance and excellent electrical properties, as well as extremely low moisture absorption and high stability

The above is the introduction of the viscosity value of SMT red glue. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.