The design performance of multiple substrates is mostly akin to that of single or double substrates. It’s essential to avoid cramming too many circuits into a confined space, which could lead to unrealistic tolerances, increased inner capacity, and potentially compromise product quality. Hence, performance specifications should encompass a thorough assessment of inner line thermal shock, insulation resistance, welding resistance, and more. Below are the crucial factors to consider in multi-substrate design.
1. **Mechanical Design:** This includes selecting appropriate plate size, thickness, lamination, inner layer copper cylinder, aspect ratio, etc.
2. **Board Sizes Optimization:** Board sizes should be optimized based on application requirements, system box sizes, manufacturer limitations, and manufacturing capabilities. Larger circuit boards offer advantages such as fewer substrates, shorter paths between components, enabling higher operating speeds, and accommodating more connections for inputs and outputs. However, designing signal line layouts on large PCBs is more challenging, often requiring additional signal layers, internal wiring, or space, and heat management. Thus, designers must consider various factors including standard board sizes, equipment size, and fabrication process limitations.
3. **Thickness Determination:** The thickness of a multi-substrate is influenced by factors like the number of signal layers, thickness of power plates, aspect ratio of apertures, pin length for automatic insertion, and connection type. Strict tolerances are challenging to achieve, with a tolerance standard of approximately 10% considered reasonable.
4. **Symmetrical Layer Arrangement:** To minimize PCB board distortion, the layers of the multi-substrate should be symmetrical. This involves ensuring an even number of copper layers and symmetry in copper thickness and foil pattern density. Additionally, the construction material used for lamination should have its radial direction parallel to the laminate’s sides.
5. **Warpage and Distortion Mitigation:** Warpage and distortion can be reduced by distributing copper foil evenly across all layers and ensuring symmetrical prepreg material distribution and thickness. The minimum distance between two copper layers should be maintained at 0.080mm to enhance stability.
6. **Copper Foil Selection:** The commonly used copper foil is 1oz per square foot surface area. However, for dense PCBs requiring strict impedance control, thinner copper foils like 0.50z are necessary. Heavier copper foils are preferable for power and ground layers, but etching them poses challenges, requiring special processing techniques.
7. **Plated Through Hole Diameter:** The diameter of plated through holes is typically kept between 0.028 and 0.010 inches to ensure adequate volume for soldering.
8. **Aspect Ratio:** The aspect ratio, i.e., the ratio of plate thickness to borehole diameter, is critical. While 3:1 is standard, higher ratios like 5:1 are often used. The aspect ratio affects drilling, de-lamination, erosion, and electroplating processes.
9. **Impedance Control:** In high-speed systems, controlling signal reflection and line length is crucial. The controllable impedance performance of electronic components is strict in multi-substrate systems. Factors influencing impedance include substrate and prepreg material dielectric constants, conductor distances, and copper thickness.
10. **Dielectric Constant Control:** The dielectric constant of substrate materials significantly impacts impedance, propagation delay, and capacitance. Lower dielectric constant prepreg materials are suitable for RF and microwave applications, minimizing signal delay and electrical loss.
11. **New Materials:** Materials like Prepreg material ROR 4403 by Rogers Company offer compatibility with standard multi-substrate constructions, providing options for RF and microwave boards alongside traditional FR-4 materials.
By adhering to these considerations, designers can optimize multi-substrate PCB designs for improved performance and reliability.
1. **Mechanical Design:** This includes selecting appropriate plate size, thickness, lamination, inner layer copper cylinder, aspect ratio, etc.
2. **Board Sizes Optimization:** Board sizes should be optimized based on application requirements, system box sizes, manufacturer limitations, and manufacturing capabilities. Larger circuit boards offer advantages such as fewer substrates, shorter paths between components, enabling higher operating speeds, and accommodating more connections for inputs and outputs. However, designing signal line layouts on large PCBs is more challenging, often requiring additional signal layers, internal wiring, or space, and heat management. Thus, designers must consider various factors including standard board sizes, equipment size, and fabrication process limitations.
3. **Thickness Determination:** The thickness of a multi-substrate is influenced by factors like the number of signal layers, thickness of power plates, aspect ratio of apertures, pin length for automatic insertion, and connection type. Strict tolerances are challenging to achieve, with a tolerance standard of approximately 10% considered reasonable.
4. **Symmetrical Layer Arrangement:** To minimize PCB board distortion, the layers of the multi-substrate should be symmetrical. This involves ensuring an even number of copper layers and symmetry in copper thickness and foil pattern density. Additionally, the construction material used for lamination should have its radial direction parallel to the laminate’s sides.
5. **Warpage and Distortion Mitigation:** Warpage and distortion can be reduced by distributing copper foil evenly across all layers and ensuring symmetrical prepreg material distribution and thickness. The minimum distance between two copper layers should be maintained at 0.080mm to enhance stability.
6. **Copper Foil Selection:** The commonly used copper foil is 1oz per square foot surface area. However, for dense PCBs requiring strict impedance control, thinner copper foils like 0.50z are necessary. Heavier copper foils are preferable for power and ground layers, but etching them poses challenges, requiring special processing techniques.
7. **Plated Through Hole Diameter:** The diameter of plated through holes is typically kept between 0.028 and 0.010 inches to ensure adequate volume for soldering.
8. **Aspect Ratio:** The aspect ratio, i.e., the ratio of plate thickness to borehole diameter, is critical. While 3:1 is standard, higher ratios like 5:1 are often used. The aspect ratio affects drilling, de-lamination, erosion, and electroplating processes.
9. **Impedance Control:** In high-speed systems, controlling signal reflection and line length is crucial. The controllable impedance performance of electronic components is strict in multi-substrate systems. Factors influencing impedance include substrate and prepreg material dielectric constants, conductor distances, and copper thickness.
10. **Dielectric Constant Control:** The dielectric constant of substrate materials significantly impacts impedance, propagation delay, and capacitance. Lower dielectric constant prepreg materials are suitable for RF and microwave applications, minimizing signal delay and electrical loss.
11. **New Materials:** Materials like Prepreg material ROR 4403 by Rogers Company offer compatibility with standard multi-substrate constructions, providing options for RF and microwave boards alongside traditional FR-4 materials.
By adhering to these considerations, designers can optimize multi-substrate PCB designs for improved performance and reliability.