Red glue is a polyene compound. Unlike solder paste, it is cured when heated. Its freezing point temperature is 150℃, at this time, red glue begins to become solid directly from paste. Red glue belongs to SMT material. This article will guide you to understand what is red glue on PCB board, what is the role of red glue on PCB, the role of red glue in PCB SMT processing and SMT red glue standard process.

What is the red glue on the PCB board?

In SMT and DIP mixed process, in order to avoid single-side reflow welding once, wave soldering once twice over the furnace situation, in the PCB wave soldering surface chip components, the center of the device spot red glue, can be soldering once on tin, save the solder paste printing process.

SMT “red glue” process? Actually, the correct name should be SMT “dispensing” process. Most of the adhesive is red, so it is commonly called “red adhesive”. In fact, there are also yellow adhesive, which is the same as we often call the “solder mask” on the surface of the circuit board “green paint”.

What is the red glue on PCB board? What is the function of red glue on PCB?

We can find that there is a mass of red glue in the middle of the small parts of resistors and capacitors. This is red glue. The red glue process was developed because there were many electronic components that could not be immediately transferred from the original DIP package to the SMD package.

A circuit board has half of the DIP parts and half of the SMD parts. How do you place the parts so that they can be automatically welded to the board? The general practice is to design all the DIP and SMD parts on the same side of the board. The SMD parts are printed with solder paste and then welded back to the furnace. The rest of the DIP parts can be welded all at once using the wave soldering furnace process because all the pins are exposed on the other side of the board. So we need two welding steps at the beginning to get everything welded.

In order to save PCB layout space, we hope to put more components into it. Therefore, SMT devices also need to be placed on the Bottom surface. In order to attach parts to the circuit board and to get the circuit board through the Wave Soldering furnace, to attach them to the soldering pad and not to fall into the hot Wave soldering furnace.

In order to reduce the technological process, we hope to complete the welding at one time. Through-hole reflow soldering is possible, but many of our plugins cannot withstand the high temperatures of reflow soldering. Therefore, through-hole reflow welding is not possible. Therefore, it is only possible to consider through-hole reflow welding for the bulk products of some large companies, because they can purchase some high-priced plug-in components that can withstand high temperatures.

And general SMD parts because has been designed to withstand temperature of reflow soldering, reflow soldering temperature is higher than the wave soldering temperature, so the SMD components left in wave soldering tin furnace, even for a short period of time also won’t have problems, but there is no way to make printing solder paste have SMD wave soldering furnace, because tin stove temperature must be higher than melting point temperature of the solder paste, This will cause the SMD part to melt and fall into the tin furnace.

Therefore, we need to fix the SMD device first, so we use red glue.

What is the role of red glue on PCB?

1. Red glue generally plays a fixed and auxiliary role. Soldering is the real welding.

2. Wave soldering to prevent components from falling off (wave soldering process). When wave soldering is used, the component is fixed to the printed board to prevent the component from falling off as the board passes through the solder groove.

3. Reflow welding to prevent the other side of the components fall off (double-sided reflow welding process). In the double-sided reflow welding process, to prevent the large devices on the welded side from falling off due to the heat melting of the solder, it is necessary to have SMT adhesive.

4. Prevent components from displacement and standing (reflow welding process, pre-coating process). Used in reflow welding process and precoating process to prevent the displacement and vertical plate during mounting.

5, mark (wave soldering, reflow welding, precoating). In addition, printed board and component batch change, with patch adhesive for marking.

What is the role of red glue in PCB patch processing?

Patch processing agent is also patch processing red glue, usually red (yellow or white) paste evenly distributed hardener, pigment, solvent and other adhesives, mainly used to patch processing components fixed on the printed board, generally dispensing or steel screen printing method to distribute. Attach the components and put them into the oven or reflow furnace to heat and harden.

Patch processing patch adhesive is the heat after curing, patch processing solidification temperature is generally 150 degrees, reheating will not melt, that is to say, the patch processing thermal hardening process is irreversible. The processing effect of the patch will be different due to the thermal curing conditions, the connection, the equipment used, and the operating environment. The patch adhesive should be selected according to the printed circuit board assembly () process.

Patch processing red glue is a chemical compound, mainly composed of polymer materials. Patch processing filler, curing agent, other additives, etc. Patch processing red adhesive has viscosity fluidity, temperature characteristics, wetting characteristics and so on. According to the characteristics of red glue in SMT processing, the purpose of using red glue in production is to make the parts stick firmly on the PCB surface and prevent it from falling off.

Patch processing red glue is a pure consumption material, not a necessary product of the process, now with the continuous improvement of surface mounting design and technology, patch processing through hole reflow welding, double-sided reflow welding has been realized, the use of patch processing patch adhesive mounting process is less and less trend.

SMT red glue standard process

SMT red glue production standard process is: screen printing → (dispensing) → mounting → (curing) → reflow welding → cleaning → detection → repair → completion.

1. Screen printing: its function is to print solder paste (solder paste) or red glue (patch glue) on the solder pad of PCB circuit board to prepare for the welding of components. The equipment used is screen printing machine (screen printing machine), located at the forefront of SMT production line.

2. Dispensing: it is the red glue point to the fixed position of the PCB, its main role is to fix the components to the PCB board. The dispensing machine is located at the front end of the SMT production line or behind the testing equipment.

3. Mounting: its function is to accurately install surface assembly components on a fixed position of PCB. The equipment used is the SMT machine, located behind the screen printing machine in the SMT production line.

4. Curing: its role is to melt the red glue (patch adhesive), so that the surface assembly components and PCB board firmly bonded together. The equipment used is the curing furnace, located behind the SMT machine in the SMT line.

5. Reflow welding: its function is to melt solder paste (solder paste), so that the surface assembly components and PCB board firmly bonded together. The reflow furnace is located behind the SMT machine in the SMT line.

6. Cleaning: its function is to remove welding residues such as flux which are harmful to human body on assembled PCB board. The equipment used is the cleaning machine, the position can not be fixed, can be online, also can not be online.

7. Detection: its function is to detect the welding quality and assembly quality of assembled PCB board. The equipment used is magnifying glass, microscope, on-line test instrument (ICT), flying needle test instrument, automatic optical test (AOI), X-ray test system, functional test instrument, etc. Position according to the inspection needs, can be configured in the production line at the appropriate place.

8. Repair: its role is to detect the failure of the PCB board for rework. The main tools used are heat gun, soldering iron, repair workstation, etc. It can be installed anywhere in the production line.