In the process of hardware circuit design, it is inevitable to make mistakes, do you have any low-level mistakes?
Here are five of the most common design problems in PCB design and how to counter them.
01
Pins are wrong
Series linear regulated power supplies are cheaper than switching power supplies, but the power conversion efficiency is low. Typically, many engineers choose to use a linear regulated power supply due to its ease of use and low price.
However, it is important to note that although it is convenient to use, it can consume a lot of electrical energy, causing a lot of heat dissipation. In contrast, switching power supplies are complex in design, but more efficient.
However, it should be noted that the output pins of some regulated power supplies may not be compatible with each other, so it is necessary to confirm the relevant pin definitions in the chip manual before wiring.
▲ Figure 1.1 A linear regulated power supply with special pin arrangement
02
Cabling error
The difference in comparison between design and routing is a major mistake that causes the final stage of PCB design. So there are a few things that need to be double-checked.
For example, device size, via quality, pad size, and review level. In short, it is necessary to repeat the confirmation check against the design schematic.
▲ Figure 2.1 Line inspection
03
Corrosion traps
Acid traps can form when the angle between the PCB leads is too small (showing sharp angles).
These sharp-angled connections may retain corrosion fluid during the corrosion phase of the board, which can remove more copper from the deposit, resulting in jams or traps.
In the later stage, the lead may be broken and an open circuit may be formed. This corrosion trap phenomenon is greatly reduced in modern manufacturing processes due to the use of photosensitive corrosion solutions.
▲ Figure 3.1 The connection angle presents an acute angle of the line
04
Monument device
When some small surface-mount devices are soldered using the reflow process, the device will form a single-ended warping phenomenon under the infiltration of solder, commonly known as "standing a monument".
This phenomenon is often caused by asymmetrical routing patterns, resulting in uneven heat diffusion across the device pads. The use of the correct DFM inspection can effectively alleviate the occurrence of monument erection.
▲ Figure 4.1 The phenomenon of monument erection in circuit board reflow soldering
05
Leader width
When the current of the PCB leads exceeds 500mA, the first wire diameter of the PCB will appear to be insufficient. With the usual thickness and width, the wires on the surface of the PCB pass more current than the wires inside the multilayer board, because the surface leads can diffuse heat through air flow.
The width of the line is also related to the thickness of the copper foil in the layer. Most PCB manufacturers allow you to choose from 0.5 oz/sq.ft to 2.5 oz/sq.ft copper foil thicknesses.
▲ Figure 5.1 PCB lead width
Here are some mistakes you can make if you're not careful:
1. Polarized capacitors, the schematic diagram and PCB have reversed the pins?
2. I forgot to connect the power supply and ground. And the opposite...
3. The wire sequence of the connector is reversed
4、RX、TX接反了。。。
5. Write a package for granted, but there is no device of this specification. Baidu library downloads datasheet, but it turns out that you can't buy this device at all.
6. Directly copy the circuit, but the device can't be bought at all.
Once a team that made smart locks, the circuit directly copied Samsung's smart lock, and it turned out that a capacitive touch button controller was difficult to buy in Korea, and there was no agency and support. Purely on your own experimentation and exploration.
7. When selecting capacitors, only the capacity is considered, and the withstand voltage is not considered, and the result is that such a large package cannot fit the capacitors that meet the specifications.
8. When choosing a resistor, only look at the resistance value, not the power consumption.
9. After drawing the PCB, don't look at the DRC report, look at the flying line with your eyes, and the flying line will really fly after returning to the board.
10. The packaging is reversed. . .
11. The solder mask layer of the heat dissipation pad is not treated
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