Thank you for your interest in our webinar on improving PCB performance with embedded resistors and capacitors. It was presented by John Andresakis of Quantic Ohmega-Ticer and Amit Bahl.
Want to watch the on-demand webinar? Click the link below.
You can ask your questions on this thread.
| Questions | Answers |
|---|---|
| How to design for embedded components into PCB Design tools (Altium, Allegro, Design Suite)? Any good resources? | To design for embedded components in PCB design tools like Altium and Allegro, you need to create an additional layer specifically for these components. This layer is referred to as a window layer and is essentially an extra artwork layer that allows you to integrate embedded components into your design. All standard PCB design tools, including Altium and Allegro, support this functionality. The key is to learn how to properly use these tools to incorporate the additional layer effectively. Moreover, most circuit board manufacturers are well-versed in working with embedded component designs. They can provide guidance and support throughout the process to ensure your design is implemented successfully. Additionally, design software providers or communities can often assist with specific questions or challenges you encounter during the process. |
| What kind of cost increase should we expect with embedded components? Would it be a similar increase to adding a layer set, or more along the lines of tight pitch BGA packages with micro vias? | The cost of PCBs with embedded components rises due to layer addition. However, this cost increase is less significant than the cost associated with the tight-pitch BGA packages. |
| How is lead time impacted if you add embedded resistors on a single layer? | Quick turnarounds, such as 1, 2, or 3-day turns, are typically not feasible. You should expect an additional 3 days to the turnaround time. |
| Are there any design rules for embedded resistors towards power dissipation limits and tolerances? | Yes, there are design rules for embedded resistors regarding power dissipation limits and tolerances. Power dissipation: 1. A power rating calculator is available to help determine the power limits for embedded resistors. 2. Resistors are rated by testing them to failure on a laminate in the open air, without heat sinks, to simulate a worst-case scenario. 3. When embedded in a PCB, copper layers and prepreg material above and below the resistor help dissipate heat, allowing it to handle more power. 4. For safety, it is recommended to de-rate the resistor’s power capacity by at least 25%. Tolerances: 1. The base tolerance of the resistor is typically around ±5%. 2. Additional etching tolerances during manufacturing can increase this to 10–15%, resulting in an overall tolerance range of 15–20%. 3. The final tolerances depend on factors such as the resistor size, board material, and manufacturing process. |
| Can you use microvias in layers that have embedded resistors or capacitors? | Yes, microvias can be used in layers with embedded resistors or capacitors. This technology does not impose any restrictions on the use of microvias. You can design clearances around the microvias as needed. However, we recommend referring to our design guide for specific recommendations and best practices. |
| Does the copper layer go over the resistor, or does the resistor get added to copper layers with overlap? | When drilling through a pad on a layer that includes resistors, we recommend offsetting the resistors from the pad by a certain distance. This ensures any heat or mechanical stresses generated during the drilling process do not affect the resistive layer, which is very thin. While these resistive layers are robust when embedded within the board, minimizing heat and stress during drilling is a best practice to protect their integrity. |
| Are there any documents available for RF characteristics of embedded resistors? | Yes, we have conducted RF characterization for embedded resistors and have some documentation available. For example, an attenuator tested up to 60 GHz shows excellent performance. Additionally, we tested the impact of resistor material located beneath traces at frequencies up to 40–50 GHz. The results showed only a minor signal loss due to the resistor material. |
| Are the Rs and Cs recognized as acceptable from a regulatory compliance standpoint? Would Underwriters Laboratories accept them? | Yes, Rs and Cs are recognized as acceptable for regulatory compliance. Underwriters Laboratories (UL) has worked with the IPC committee on embedded resistors and capacitors to establish specifications for these materials. If your product is designed with these materials and undergoes the standard UL testing, it will meet UL requirements. |
| What thicknesses are available when adding a resistive layer? (impact on overall stack-up thickness) | Since the resistor material is very thin, it’s typically supplied on 1/2 oz. copper, although it can’t be supplied on 1 oz. copper. You would usually incorporate it into a signal layer, adding minimal thickness. For example, the worst-case scenario for a 10 Ω/square material is about a micron in thickness, which is almost negligible. If you need to add an additional signal plane, it would add just the 1/2 oz. copper. In the case of embedded capacitors, the thickness is actually reduced due to the decreased spacing between the power and ground planes. |
| What artwork modifications are recommended for the designer to mitigate the tolerance issues? Is this handled by the PWB vendor to meet its specific process tolerance? | To address tolerance issues, artwork modifications are crucial. Designers need to consider two primary challenges affecting resistance tolerance: 1. Overall resistance tolerance – This is influenced by the width and length of the etched features and the registration accuracy. 2. Registration challenges – During the two-step etching process, there may be slight misregistration between the first and second etches. To mitigate these issues: 1. Use precise techniques like laser direct imaging to achieve good registration, typically within a 1-mil placement tolerance. 2. Design electrodes slightly larger than the resistor area to ensure the resistor remains fully within the electrode boundary, preventing deviations in resistance values. 3. Aim for larger resistor dimensions where possible. For example, while 5-mil-wide resistors may be used in some applications, they result in higher tolerance variability. Keeping the width and length above 10–20 mil significantly improves performance and reduces tolerance challenges. |
| For example, If I need an 8-layer board for my design, to incorporate embedded passives, will I need 10 then? | For designs incorporating embedded resistors, the answer is typically no—you wouldn’t need additional layers. Embedded resistors are placed where they would normally exist in the circuit, such as on the surface, but instead are moved into the board. This eliminates the need for vias and does not add extra signal layers. However, when incorporating embedded capacitors, the situation can vary. If your design doesn’t already include tightly coupled power and ground planes, you may need to add an extra reference or ground plane to achieve effective operation. For instance, designs may move from a 12-layer board to a 14-layer board to accommodate this additional plane. The good news is that these added layers are very thin and don’t significantly increase the board’s overall thickness. A typical stack-up might change from reference plane → signal → signal → ground plane to reference plane → signal → ground → signal → reference plane → power → ground plane. While adding layers may increase complexity, the improved performance of embedded capacitors often justifies the additional layers. |
| Does the resistive layer cover the whole PCB then? | Yes, the resistive layer does cover the entire PCB layer. It is applied as part of a subtractive process. Initially, the resistive material is deposited over the entire copper layer. During the first etching process, the excess resistive material is removed, leaving it only under the traces. The areas where resistors are needed are then opened up on the traces. Any parts of the resistive layer not required for functionality are removed, ensuring the material only remains where it is essential. The higher the resistor density on the board, the more cost-effective it becomes. In applications like MEMS microphones, high resistor density leads to significant cost savings. However, in many designs, using embedded resistors isn’t solely driven by cost. Factors such as performance improvements or the ability to reduce board size often play a more significant role. It’s important to note that this approach is highly design-specific and may not always result in a one-to-one cost-saving benefit. |
| In that case though, we can’t use signal layer for both routing and resistors then, correct? Because we would have high resistance material on that layer? | It is possible to use a signal layer for both routing and resistors. This is because the resistive layer is extremely thin, and the copper used is low-profile. Testing up to 40 GHz has shown that the additional signal loss caused by the resistive layer is minimal—only fractions of a decibel per inch. As a result, many high-speed signals are successfully routed on these layers. In fact, this approach is widely used in products with PTFE (teflon)-based materials, where high-speed signal traces and electromagnetic absorption applications are common. |
| Where can I find examples of the EM absorber application? | If you’re interested in examples of EM absorber applications, feel free to contact me. We have examples where this technology is used in applications like AEM absorbers for cards and other similar designs. It’s important to note that designing EM absorbers is as much an art as it is a science. The effectiveness depends heavily on factors such as the pattern design and the material stack-up. By adjusting these elements, you can manipulate the frequencies that are allowed to pass through or are reflected, tailoring the absorber’s performance to your specific needs. |