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As data and connectivity continue to be popular themes in tech, engineers are increasingly tasked with packing more features into smaller products, which often leads to deeply integrated electromechanical designs and complex assemblies. This guide aims to outline a framework for electrical and mechanical engineers to identify easily overlooked PCB design issues, minimize revision cycles, and help keep all of those sweet features in your new product.
PCB Design: Where Mechanical & Electrical Engineering Intersect
您可能已经知道，与具有专业背景的个人团队开发产品时，沟通至关重要。尽早向团队传达您的需求conflicting design requirementsand address them while designs are still in the CAD or schematic phase, resulting in a solution that’s cheaper, easier, and less painful to design.
The Prerequisites
假设您的团队有明确合理的产品要求，那么个人可以制定初始的机械和电气设计。信封约束和工业设计将推动机械设计。人体工程学，行业法规和材料属性的限制都是因素。产品要求中概述的功能将推动电气设计。
一旦机械工程师（ME）具有工作机械设计，并且电气工程师（EE）具有功能性示意图，团队可以开始设计印刷电路板（PCB）。
PCB大纲和保留地
该过程的第一步是就初始的PCB大纲达成一致，该大纲使设计团队能够尽早就PCB的尺寸和形状达成一致。我应该提供具有以下关键元素的图纸：
- Board Outline
- Areas with Height Restrictions
- Keepouts for Parts
- 痕迹的保留
董事会轮廓很明显 - 这是PCB制造后的最终形状，很大程度上取决于机械设计。通常，鉴于机械设计中的预期位置，ME可以从提供最大PCB尺寸的图纸开始。如果示意图设计允许，ME可以与EE合作以将PCB轮廓减少到最小的可能区域，这将有助于降低材料成本。
需要考虑的事情：与有机“弯曲”轮廓相比，矩形板的轮廓将导致成本更低，这是由于浪费的PCB材料较少，并且需要更多的机器时间来驶出有机形状。在通信板轮廓时，应包括电气组件的最大高度约束。在许多情况下，由于机械限制，PCB上的每个位置的最大允许高度都不会相同。
The outline drawing should note regions of the PCB that have height restrictions smaller than the maximum in order to avoid interference issues during assembly. “Keepouts for Parts” are areas where the mechanical enclosure touches the PCB or comes so close that there’s not enough clearance for small components. These areas should be communicated in a similar way as those with height restrictions.
最后，“痕迹的保留”是PCB的区域，无法具有任何痕迹。这可以应用于特定层或所有层。对于MES而言，设计周期初期关注的主要区域是金属零件位于PCB附近，安装功能和板的边缘，包括任何内部切口。
应该总是有一个最小的距离edge of the board that can’t have any traces. The distance is dependent on the Voltage, Current, and Dielectric material of the PCB and is aimed at preventing electrical arcing.
If your product requires certification from a registered Safety Body, they will have minimum guidelines specific to your application. Otherwise, the latest IPC-9592B document is a good place to start. Note: If you’re using metal hardware to secure the PCB, include extra keepout space to take into account the diameter of the screw head.
It’s a common mistake to just offset from the through hole diameter, which can result in interference or shorting.
布局
在这一点上，EE可以开始放置连接PCB上电气组件的轨迹。最好开始将所有组件分组为没有高度限制并放慢移动的单个组件或由小部件组成的整个电路的区域，并有限制。我和EE应该聚在一起，确定大型，稀有或高风险组件的列表。
铺设这些部分时，应格外小心。团队所有成员都应审查规格表；并且应在CAD中嘲笑零件，以确保它们在没有问题的情况下集成到机械设计中。EE应确定有特殊要求的PCB区域：AC与DC电路，电容感应，天线等。通常，这些特殊的布局区域限制了组件的放置。
布局完成后，大多数专业的软件包将使您以3D文件格式导出PCB，当组件紧紧打包时，这确实很有帮助。我应该将3D文件加载到机械组件中以进行审查。如果团队中的每个人都签字，并且一切都适合一个PCB，那就恭喜！这是你幸运的一天。
Complex Solutions: How to fit too many things into not enough space
归根结底，PCB布局全都与表面积有关。您只有这么多的区域可以放置组件，并且随着连接的设备变得更加复杂，您通常没有足够的空间将所有内容都放在一个PCB上。幸运的是，有很多选择可以帮助您解决此问题。
以下是一些常见解决方案的利弊。
将图层添加到PCB
In this case, there’s enough physical space to fit all of the components onto the board, but once the EE starts to route the traces and account for the required spacing to prevent electrical arcing, you can’t fit everything into the limited surface. Your best option is to add layers to the PCB, which will add some cost to your board. It’s fairly common for a PCB to have 1-8 layers, but they can have more if your design requires it.
注意：添加层会增加厚度或PCB，并可能影响您的整体组件。
女儿董事会
When you run out of space on your main PCB, the motherboard, usually the best and most cost-effective option is to move an entire circuit to a completely new PCB, the daughter board. Ideally, you want to move entire circuits over to a daughter board to reduce the number of required connections back to the motherboard. This will add some additional cost to your assembly, due to the added PCB, and will add complexity, because you need to find a way to mount the daughter board in your mechanical assembly and connect it to the motherboard.
这通常是最好的选择，因为它易于设计具有可靠的安装功能和可靠的现成解决方案以将板连接在一起的PCB。
Note: this is also a good option if your design requires a sensor,按钮，或切换到远离主PCB的位置。
Move Large Components off the PCB
在某些情况下，您可能只有一个或两个大型组件 - 可能是过滤电容器，电感器或第三方传感器模块，可阻止您设计一个小型紧凑型PCB并将其滑入机械包装的一个漂亮的小角落。如果它可以释放出您的设计，请不要害怕发挥创造力，并在包装中的其他地方移动其中一个或两个组件。
If your package will be injection molded, you can design custom mounting features to hold these components directly into your package. Then, connect them back to the PCB with flying leads.
将所有内容连接在一起
现在，我们已经在母板和一个或多个女儿董事会之间将电路分开了，我们需要以一种既具有成本效益又可靠的方式将所有内容联系在一起。如果您需要两个PCB之间的电路连接，并且有空间，则最佳选择是水平或垂直标头。这是一个常见的解决方案，有许多现成的选择。不利的一面是，标题本身通常会在PCB上占据很多表面积。
If a header doesn’t work in your design, the next best option might be a custom cable assembly. Again, these are common and provide a more flexible solution than headers, because the cable assembly can be tailored to your needs.
Cables can be any length you need. Connectors can be placed anywhere on either PCB and don’t necessarily need to match up like headers. This will add slightly more cost than headers because of the labor required to make the cable assembly. Keep in mind the order of operations of product assembly!
可以在CAD空间中设计一个无法合理组装的解决方案，如果您在捕获之前走得太远，这可能会导致重新设计的疼痛。要注意的另一件事是：由于最小间距以防止电动电弧，因此标头和电缆组件连接器更大。大型连接器通常不会在紧密包装的组件中工作，这就是为什么最好将低功率电路移至女儿板的原因。
When space constraints outweigh cost constraints, your best option is probably a flex connector or circuit, which are essentially printed circuit boards, but instead of using fiberglass as the substrate, the circuits are printed on flexible kapton. This lets you bend and fold the connector as needed, with the benefit of only being 0.1-0.2 mm thick for a single layer circuit.
像电缆组件一样，Flex电路是针对您的设计进行定制的，并且可以在大量上具有成本效益，但是由于切除Flex电路的形状所需的工具，它们的数量较低。Flex连接可以直接焊接到PCB，也可以使用ZIF连接器。
主要要点
PCB设计的许多因素都需要来自多个利益相关者的输入。能够在产品开发生命周期的早期识别和脱离风险的空间约束将最大程度地减少正确的迭代次数。当一切都不适合一个PCB时，成本和可靠性应始终是主要问题。希望这本剧本为您提供了PCB设计创造性所需的灵感。
