Hello everyone and welcome to this article. Today we are going to have a look at double-sided Surface Mount Technology (SMT) assembly and how it works. It is good to remember that Surface Mount Technology is used in attaching electrical components to a printed circuit board where the components are attached on the surface of the PCB without drilling holes. The components attached can be either leaded or non-leaded. Also, you need to remember that double-sided PCBs, are a type of board that provides both sides with conductive layers for the components. This means that both the bottom and the top layers have conductive paths. Both sides of the board have a covering of copper which acts as the current-carrying material. Now let us have a look at how the double-sided SMT assembly is done.

What SMT assembly is

SMT assembly stands for Surface Mount Technology assembly and it is classified as a type of soldering technology that employs the use of the reflow soldering technology or any other defined process to mount electronic components on a printed circuit board. This process being complex has to be divided into single-sided and double-sided SMT. And in this article, our focus is on double-sided SMT.

SMT assembly by PCBGOGO

Defining double-sided SMT

This is a process that makes use of double-sided PCBs. One side of the board will have a major IC chip while the other side will be composed of IC components. The design process is somehow complex since it also involves the use of complex components.

Before we can have a look at the double-sided SMT assembly, let us first understand how the SMT assembly process is done in general.

SMT Assembly Process

1. Dispensing

Since the type of board that is generally used in this process is the double-sided printed circuit board, to prevent the components that were soldered on the input side of the board from undergoing melting and re-sold off because of remelting of the solder mask, it is advised that a dispenser is installed at the input surface. A water droplet at the input of the printed circuit board is employed to fix the electronic components to the board. A dispenser is a piece of equipment used and it is placed at the forefront of the production line or sometimes behind the equipment used for inspection. If the components are designed to appear to be too large, then the fabricators will have to use manual dispensing.

2. Component placement

The purpose of this process is to make sure that the surface mount components are accurately fixed at the exact required position on the printed circuit board. A Pick&Place machine is used to ensure that the process is achieved. This machine is located behind the machine used for printing on the production line.

Pick&Place machine in PCBGOGO

3. Curing

This one is used to aid in melting the patch glue and this helps to ensure that the components and the printed circuit board are strongly bonded together. The curing oven is the special equipment used in the process and it is located behind the machine for placement in the surface mount technology assembly line.

4. Reflow soldering

This does the melting of the solder paste so that to ensure that the SMT components and the printed circuit boards are bonded together. The reflow soldering furnace is the equipment that makes this possible and you will find it behind the placement machine in the production line.

Reflow oven in PCBGOGO

5. Cleaning

This is the process where the harmful soldering residues such as the flux are removed from the SMT assembled printed circuit boards. Here, the washing machine is used as the equipment and the location for it is not fixed at any point on the production line since it can be used along the line.

6. Inspection

Here the welded board assembly quality is put to test to ensure that whatever was done is correct and of great quality. The magnifying lens, online tester, microscope, AOI, flying probe tester, etc. are used to ensure that the process is done well. THIS is positioned at any suitable place along the production line depending on the need of the inspection.

AOI in PCBGOGO

7. Rework

Here, we involve PCBs that have a failure detected. The PCB is reworked to remove the failure. The tools involved are soldering irons and it is configured along the production line at the desired position.

Now let us have a look at the double-sided SMT assembly;

Double-sided SMT Assembly

The double-sided SMT assembly process is almost similar to the general assembly process but only a few steps will be added. The following steps are involved. Most of these steps have been described in the general method above and I will not be repeating them.

1. Incoming Inspection

Here the inspection of the assembly files is done to ensure they are to the standards of the designer.

2. Screen solder paste printing the printed circuit board side A.

Side A is the first side to be printed. The process on side A is done similarly to what is done while doing the single-sided SMT assembly.

3. Surface Mounting

4. Drying

5. Reflow soldering on Side A of the PCB

6. Clean out

7. Plate turnover

The turnover is special to allow printing of side B of the double-sided PCB.

8. Dispensing of the surface mount adhesive on the printed circuit board side B.

9. Surface mounting

10. Drying

11. Wave soldering the PCB side B

Here wave soldering is preferred as compared to reflow soldering because it will protect the printed side A from remelting.

12. Cleaning out

13. VI & AOI

This is where the inspection for quality is done to make sure that the design has no defects.

14. Reworking

Summary

Double-sided SMT assembly is a very necessary process when it comes to assembling PCBs with more than one layer. Mostly used when the top and bottom layers of the PCB are to be printed. The process and the machines used in the process have been highlighted.

PCBGOGO is a fabricating house that could solve your PCB fabrication challenges. They have an SMT production line that would do all types of PCB assembly .