1. **PCB Layout and Design: Production Requirements**
The requirements for plate thickness, copper thickness, processes, solder mask/character colors, and other specifications should be clearly defined. These requirements serve as the foundation for producing the board, so R&D engineers must document them with precision. Based on my experience with customers, Gree has done a particularly good job. The technical specifications in their documents are very clearly written. For example, although we typically use green solder mask ink and white characters, this is explicitly noted in their technical requirements. On the other hand, some customers may not specify these details if they are flexible or prefer to avoid them. If no specifications are given, manufacturers will often proceed with proofing production based on their standard practices, which may not always meet the exact needs of the customer—especially when certain manufacturers have unique requirements that need to be addressed in advance. Failure to document these specifics can lead to confusion and issues later, such as manufacturers seeking clarification or not meeting the required standards upon delivery.
2. **Drilling Design**
The most significant challenge in drilling design is managing the smallest hole size. Typically, the smallest holes on a PCB are via holes, which directly impact costs. In some cases, vias could be designed with 0.50mm holes, but if they are reduced to 0.30mm, the cost increases significantly. PCB manufacturers tend to raise prices when the cost per hole is higher. Additionally, having too many vias can be problematic—on some PCBs, such as those used in DVDs and digital photo frames, vias can take up the entire board area, leaving little room for other elements. I have worked on boards with up to 1,000 holes, but I believe 500-600 holes is more optimal. Some may argue that additional vias improve signal integrity and heat dissipation, but this must be balanced against cost considerations. I can provide an example: Our company has a customer in Shenzhen who manufactures DVDs at a large scale. Initially, cost was a major issue for both sides. After collaborating with the R&D team, we increased via sizes wherever possible and eliminated some vias from large copper areas. For instance, we replaced heat dissipation vias in the middle of the main IC with four 3.00mm holes. This change significantly reduced drilling costs. By making these adjustments, we were able to reduce drilling costs by several dollars per square unit, leading to a mutually beneficial outcome for both parties. Another issue involves slots—such as 1.00mm x 1.20mm slots—where manufacturing becomes challenging. First, controlling tolerance is difficult, and second, the drilled slot is often not perfectly straight but slightly curved. We’ve encountered situations where such minor issues with slot quality led to a deduction of $1 per unit, despite the boards only costing a few cents in RMB. After discussing this with the customer, we switched to using 1.20mm round holes instead, which solved the problem.
3. **Circuit Design**
1. **Line Width, Line Spacing, Open Circuits, and Short Circuits**
The most common issues faced by manufacturers often involve line width, line spacing, open circuits, and short circuits, among others. In general, for more conventional boards (excluding special designs), larger line widths and spacings are preferable. I’ve come across some documentation that shows traces with several bends in the middle, along with multiple lines of the same width and size, yet with varying spacings. For example, the spacing might be as small as 0.10mm in some areas and 0.20mm in others. I believe R&D should pay closer attention to these details during the routing process. Additionally, there are cases where the gap between certain circuit pads or traces and large copper areas is just 0.127mm, which makes it more challenging for manufacturers to manage the film. Ideally, the gap between pad traces and large copper should be 0.25mm or more. There are also situations where traces have minimal safety clearance from the board edge or V-CUT areas. While manufacturers can sometimes move traces in these cases, good design practice is essential to avoid issues. Some traces may even appear to be part of the same network but are not connected, while others that should be connected are mistakenly isolated. These discrepancies often lead to open or short circuits, and it is not uncommon for manufacturers to identify these issues during communication with R&D, requiring data revisions. Experienced engineers may spot these problems easily, but those less experienced may only follow the design documents, leading to additional steps such as re-proofing or correcting the layout manually. For boards that require impedance control, it’s crucial that R&D clearly defines these requirements; otherwise, they may not be met in production. Furthermore, some designs include through-holes on SMD pads, which can result in soldering defects like tin leakage.
2. **Solder Mask Design**
Common issues with solder mask designs include the improper exposure of copper areas that should be left open. For example, solder masks should be removed from copper areas to facilitate heat dissipation or to expose copper on high-current traces. Typically, these solder mask modifications are made on the Soldermask layer, but in some designs, R&D creates new layers on the mechanical or forbidden wiring layers, which can be confusing without clear instructions. To avoid misunderstandings, it’s best to place these modifications on the TOP Soldermask or BOTTOM Soldermask layers, as this makes the intent clearer. Additionally, it’s important to specify whether the green oil bridge around ICs should be retained, and providing such explanations is highly recommended.
3. **Character Design**
The key consideration in character design is ensuring the proper width and height for legible markings. Some boards have inconsistent character sizes for the same components, which looks unprofessional from a manufacturer’s perspective. It is advisable to follow the example of motherboard manufacturers, where component markings in rows are consistent and visually appealing. Ideally, character sizes should be at least 0.80mm by 0.15mm, as this is easier to manufacture using silk-screen printing. Another issue arises with large white silk-screen blocks, such as those over crystal oscillators or power strips. Some manufacturers use white oil covers over the pads, which can block pad exposure; these cases should also be clarified in the design. I have also encountered errors where the silk-screen positions were incorrect, such as resistor and capacitor designators being swapped, although these errors are rare. It’s also important to specify any required logos, such as UL, RoHS, PB, manufacturer logos, and serial numbers.
4. **Shape Design in PCB Layout**
In modern PCB design, irregular shapes are more common than rectangular ones. However, there are often multiple ways to define the board’s outline, making it difficult to choose the best option. Additionally, to improve equipment utilization (e.g., for SMT), V-CUTs may be necessary, but the pitch of the board can vary. Some designs include spacing between V-CUTs, while others do not. Although it may be fine to create samples and prototypes in the first factory, later production can become problematic if a second supplier is involved. If the second supplier doesn’t match the first factory’s design, issues with steel mesh alignment can occur. Therefore, unless there are special requirements, it is best to avoid spacing between V-CUTs. Furthermore, some design files include small rectangular holes on the outline layer intended for slots to be drilled. This is more common with files created in PROTEL software, though PADS generally handles this better. Manufacturers may misunderstand these small holes if they are placed in the shape layer, potentially leading to confusion and incorrect drilling or treatment as NPTH (Non-Plated Through Hole) attributes. Mismanagement of PTH attributes can cause further complications.
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