PCB News - What is the SMT red glue process? When should red glue be used? What are the restrictions?

What is the SMT red glue process? When should red glue be used? What are the restrictions?

What is the SMT "red glue" process? In fact, the correct name should be the SMT "dispensing" process. Because most of the glue is red, it is commonly called "red glue". In fact, there are also yellow glues. "Solder mask" is the same as "green paint". It can be found that there is a red glue-like object in the middle of the small parts of resistors and capacitors. This is red glue. It was originally designed to stick the parts on the circuit board, and then the circuit board can pass through the waves. The wave soldering furnace allows parts to be tinned and joined to the solder pads on the circuit board without falling into the hot wave soldering furnace.

The red glue process was developed because there were still many electronic components that could not be transferred from the original plug-in (DIP) package to the surface mount (SMD) package immediately. Imagine a circuit board has half DIP parts and the other half is SMD parts. How do you place these parts so that they can all be automatically soldered to the board? The general practice is to design all DIP and SMD parts on the same side of the PCB board. SMD parts are printed with solder paste and soldered in the reflow furnace, while the remaining DIP parts are exposed on the other side of the circuit board because all solder feet are exposed., So you can use the wave soldering furnace process to solder all the DIP solder feet at one time.

Later, a clever engineer thought of a way to save space on the circuit board, that is, to find a way to put parts on the side that originally only had DIP parts feet and no parts, but most DIP parts have too many gaps in the body, or The part material cannot withstand the high temperature of the soldering furnace, so it cannot be placed on the side of the soldering furnace. However, the general SMD parts have been designed to withstand the Reflow temperature, even if they are immersed in the wave soldering furnace for a short period of time. There will be no problem, but there is no way for SMD to pass through the wave soldering furnace for printing solder paste, because the temperature of the soldering furnace must be higher than the melting point of the solder paste, so the SMD parts will fall into the soldering tank due to the melting of the solder paste Inside.

Of course, some engineers later thought of using thermosetting glue to adhere SMD parts. This glue needs to be heated to cure. It just happens to be able to use a Reflow furnace to solve the problem of parts falling out of the tin bath. Red glue was born., So the size of the circuit board has been further reduced.