With the circuit design and materials already in place, the only thing missing is these plug-ins to clear the PCB!
From product conception, theory and circuit design, parts selection to actual production, etc., every step is interlocking. It seems that the circuit diagram is perfectly designed and the materials are selected, but finally encounters problems during the production of printed circuit boards (PCB). There are many limitations and difficulties. Which step did it go wrong? Should we reselect materials or redesign? In DigiKey's powerful tool library, as long as you make good use of some small tools to reduce mistakes and worries, electronics and engineering will also become handy. Next, we will introduce several design-level gadgets that can help you easily create products.
Printed circuit board (PCB) design
After the circuit simulation test of the solderless test board , the next step is the circuit design of the PCB. PCB is a sandwich board composed of an insulating layer and a conductive copper layer, which includes signal traces, power supply and ground layers. The trace layout design is as strict as the circuit design. The integrity of the system needs to be considered, and the circuit characteristics must be understood to make decisions. Corresponding circuit design. Understanding the trace characteristics can help engineers quickly determine the circuit and layer requirements of the PCB. Refer to the following checklist for PCB design for two different systems.
The following is a sensing system using a 12-BIT microcontroller, whose circuit includes analog-to-digital (A/D) conversion, LCD display and 5V external power supply. Although the current carrying capacity is not high, the wiring design of analog and digital circuits needs to be separated independently, and the checklist is provided for reference.
1. Check the position of the device and connectors. Ensure that high-speed devices and digital devices are close to the connector.
2. There must be at least one ground plane on the circuit board.
3. Make the power traces wider than other traces on the board.
4. Check the current return path and look for possible noise on the ground connection.
5. Bypass all devices correctly. Place the capacitor as close to the device's power pins as possible.
6. Keep all traces as short as possible.
7. Trace all high-impedance traces and look for possible capacitive coupling issues between traces.
8. Ensure that signals in mixed-signal circuits are properly filtered.
(Source: Microchip)
As well as some basic rules for PCB circuit design in making a high current power supply controller using MOSFETs. Since different line areas have different current-carrying requirements, cost-effectiveness can also be considered in designing lines for different areas.
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When powering a socket design, parts should be placed together.
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Provide sufficient current to the load.
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Noise immunity of load and sense circuits.
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Current sensing considerations.
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Consider heating up.
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Consider trace impedance to reduce derating effects on high-current rail groups.
(Source: Texas Instruments)
From the above two completely different types of product designs, we can see that there are certain requirements for the width of the traces, including temperature changes, current carrying capacity and impedance values. Next, we will introduce the following small tools about PCB design to help you quickly calculate the required trace width and trace impedance.
This tool uses the formula provided by the IPC-2221 standard to calculate the width of a copper printed circuit board conductor, or "trace," required to carry a given current while keeping the temperature rise of the trace below specified limits. Additionally, if the trace length is known, the total resistance, voltage drop, and power loss due to the trace resistance are calculated. First, calculate the area (A) using formula (1):
In the IPC-2221 standard, for the inner layer, k = 0.024, b = 0.44, c = 0.725Z; for the outer layer, k = 0.048, b = 0.44, c = 0.725, where k, b and c are determined by the IPC-2221 The constant obtained by curve fitting the curve. Then, calculate the width (W) using formula (2). (Note: Traces on the inner layers of the circuit board require much greater width than traces on the surface of the board.)
As long as you enter the required values on the calculator, you will quickly get the required printed line width (W), resistance value and voltage drop power loss when designing inner layer traces and exposed outer layer traces. The resulting values for the two routing designs are compared side by side. Taking the power controller mentioned above as an example, if the current carrying requirement (I) is set to 0.8A, the ambient temperature is 25°C, and the copper layer thickness (t) is 0.035mm (such as
MG Chemicals' 587 model prototype board
, 1 ounce of double-clad copper), a TRise of 10°C, and a trace length of 10” (the expected length on a 6”4” PCB without the trace being close to or over the heat sink area ).
Results are estimates only and actual results may vary depending on application conditions. The inner layer and the outer layer are displayed at the same time, forming a strong contrast, which not only facilitates engineers to design circuits, but also provides you with economic benefits, because the voltage drop and power loss of using the inner layer will be lower, and its width requirement is relatively large. , that is, the cost will be higher. You can modify parameter values at any time according to your requirements, and the results will be updated instantly and are easy to compare.
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Trace type
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legend
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describe
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microstrip line
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It refers to a simple double-sided PCB design, with a ground layer on one side, a dielectric layer in the middle, and signal traces on the other side to control impedance. This geometry is called a surface microstrip, or more simply a microstrip.
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Embedded microstrip line
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结构与微带线类似，只是将信号走线置于介质层中间。嵌入式有较高保护，低阻抗，但较难解耦，及阻抗值偏低，影响匹配。
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边缘耦合微带线
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普遍用于差分电路，例如低压差分信号。此走线设计具有降低电磁干扰的一些优势。相反的低压差分信号电流产生的电磁干扰场往往会相互抵消。
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带状线
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现时的PCB 设计多数都是多层
PCB。带状线这种布置是将信号走线嵌入电源层和接地层之间。低阻抗交流接地层和嵌入的信号走线形成对称带状线传输线。
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非对称带状线
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非对称带状线与带状线类似，只是将介质层中的信号走线靠近其中一面导电层，与接地层和电源层形成不对称的距离，一般会将信号走线靠近接地层。
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宽边耦合带状线
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普遍用于拥挤BGA区域，由两条平行的走线组合而成，具有相等的宽度、走线之间的距离和与导电层的距离。对于在相邻信号层上布线的差分对走线，如果存在任何走线重叠，则宽边耦合会更强。
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边缘耦合带状线
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由两条信号走线组成，两条信号走线都是对称带状线，走线之间存在一些耦合，指在同一信号层上布线的两个差分对。
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表一. 走线类型对应表
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走线宽度（w）= 8.693 mil、走线厚度（t）= 0.035 mm、板高度（h） = 0.79 mm
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介电常数（ε r ）= 4.2（ 参考 规格书 ，Dielectric Constant @1 GHz）
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该代码系统会区分大小写。您会注意到，系统通过使用一些小写字母，减少混淆情况，例如 I 和 O，它们很容易与1 和 0混淆。
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电容代码不像其他代码格式一样等同电容值。每个字母代码有相对应的数值，详情可参考下表。
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请注意，虽然该代码系统仍然以「pF」为单位，但该乘数代码与其他两种格式中所使用的代码有所不同，例如代码 「9 」= 「0.1」。
总结
Participate in welfare activities and win selected practical gifts
From now until March 26, we have a welfare event [Revealing the Essential Tools for PCB Design!
], invite you to the designated post on DigiKey Technology to share your PCB design experience and tell us your thoughts after using the tools introduced above.
Those with the most exciting content will have a chance to win teacher Lin Chaowen's book "PADS9.5 Practical Strategy and High-Speed PCB Design" (valued at ¥45.76).
In addition, those who leave messages and share designated event tweets to the engineer exchange group with more than 100 people will have the opportunity to take home Ai Qingchun’s latest electric cooker.
For more event details, please check the second event tweet this week >>
For more technical information on PCB design and resistor and capacitor confirmation, please click on the link below.
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