TERMINOLOGY IN CIRCUIT DESIGN - PART 3
The concepts discussed in Part 1 and Part 2 give us definitions related to circuit design. A PCB that wants to be realized then it will be manufactured, assembled, and tested. Part 3 below introduces some concepts in the process.
1. Paste stencil
It is a thin metal or plastic and perforated in the pad of the Surface-Mount Device (SMD).
Figure 1: Metal Paste stencil
This metal paste is quite expensive. We can use the clear plastic sheet which is cut by laser as shown below.
Figure 2: Plastic paste stencil
2. Solder paste
We put the paste stencil on the circuit and spread the solder paste on it. The solder paste will be remained on the PCB at the perforated position. These are the positioning pads.
Figure 3: Stencil solder paste by hand
The result of this process:
Figure 4: Circuit is stenciled
If you want to save money, you can pump solder paste directly to the PCB. The result depends on your ingenuity.
Figure 5: Solder paste without Stencil
In industry, the placement of the surface-mount device is performed by a pick and place machine. Even more modern machines can assemble the through hole components.
The following video illustrates this process.
After using the machine, we have the result as shown below.
Figure 6: Components are arranged using the pick and place machine
4. Reflow soldering
The purpose of this process is to connect the pins of surface-mount components to the pads on the circuit by melting the solder paste.
If you solder a prototype or a small amount of PCB, you can use the hot air rework station in Fig 7.
In process, we should refer to the time and temperature allowed for each component. You can look up this parameters in the datasheet.
Figure 7: Hot air rework station
If you need to assemble larger quantities of PCB, then you can use the reflow oven which is shown below (Figure 8).
Figure 8: Reflow oven
To save money, you can reuse an infrared oven. It is equipped with a timer and a temperature sensor. Perhaps this is a funny project.
Figure 9: Handmade Reflow Oven
5. Pogo Pin
Pogo pin is a metal bar that is used making temporary connection for PCB testing. The input and output signals in this process often complies with the complex rules. Therefore, the operation should be performed by the software. Input signal is gotten through Pogo pin.
The structure of Pogo pin is as following:
- Connectors have a variety of shapes, match the pads of each component.
- Internal spring increases the possibility of contact with the pads. Because the height of the points on circuit is not much different, the elasticity of the springs can solve this problem.
You can see Pogo pin as a ballpoint pen.
Figure 10: Structure of Pogo Pin with In-circuit Test
The diversity of shape and size of Pogo pin is shown in the image below.
Figure 11: Kinds of Pogo Pins
In-Test Circuit includes Pogo pins to test the product after assembling.
Figure 12: In-test circuit using Pogo pins
6. Solder pot
Solder pot is a tin tank used to weld through hole components by dipping the assembled board into it. This tools is suitable for relatively small quantities of products.
Figure 13: Mini-solder pot
The following video illustrates the process of using a solder pot to weld componenets.
Solder pot for large quantities of PCB:
7. Wave solder
Wave solder is a fast, easy-to-perform method of welding components. It's used in industrial process.
The through-hole components are placed on the circuit board. After that it is put onto the line and passed through a melting tin tank.
This process is shown in the video below:
Thank you for your time and looking forward to your comment.