**Foreword**
Mobile devices are continuously evolving toward being lighter, thinner, and more compact. The smartphone industry is a prime example of this trend. Looking at the size evolution of several generations of iPhones, we can clearly see a consistent move toward thinner designs (Figure 1). With the rise of the Internet of Things (IoT) and wearable technology, this trend has reached new extremes.
**Figure 1: iPhone Thickness Changes**
The miniaturization of mobile phones has been driven by advancements in various technologies, including System-in-Package (SiP), PCB design, and display innovations. Among these, EMI shielding plays a crucial role. Traditionally, smartphones have used metal shielding covers to protect sensitive components from electromagnetic interference. However, these covers take up valuable space on the PCB and inside the device, creating challenges for further miniaturization.
A newer solution—Conformal Shielding—offers a more efficient alternative. This technique integrates the shielding layer directly with the package, giving the module its own shielding capability. Once the chip is mounted on the PCB, no additional shielding is required, freeing up both space and cost. As shown in Figure 2, most of the chips on the iPhone 7, such as WiFi/BT, PA, and Memory modules, utilize conformal shielding, enabling high integration, reduced size, and improved performance.
**Figure 2: Modules with Conformal Shielding on the iPhone 7 Motherboard**
**SiP Package Conformal Shielding**
Shielding in electronic systems serves two main purposes: meeting EMC (Electromagnetic Compatibility) regulations and preventing interference between components. The traditional approach involves placing a shield on the PCB, which can complicate mass production and reduce repairability. In SiP packages, similar methods like overmolded shielding are also used, but they often increase the height of the module and introduce additional manufacturing costs and complexity.
**Figure 3: Traditional Shield Module and Overmolded Shield in SiP Package**
Conformal shielding in SiP packages addresses these issues effectively. As seen in Figure 4, it conforms to the shape of the package without adding extra size or height, making it ideal for ultra-thin designs.
**Figure 4: Conformal Shielded SiP Package vs. Traditional Shield**
**Conformal Shielding Performance**
Conformal shielding delivers exceptional performance, with shielding effectiveness reaching up to 12 GHz in the far field, 6 GHz in the near field, and over 30 dB in the 10 MHz–100 MHz range. As demonstrated in Figure 5, real-world test results confirm its effectiveness in reducing EMI and improving signal integrity.
**Figure 5: Test Results of Conformal Shielding**
**Conformal Shielding Process**
Currently, three main processes are used for conformal shielding: electroplating, spraying, and sputtering. Each has its own advantages and limitations. Sputtering, for instance, offers excellent coverage and uniformity. The process flow for sputtering is illustrated in Figure 6.
**Figure 6: Sputtering Process for Conformal Shielding**
**Conformal Shielding Application**
Conformal shielding is widely used in SiP modules such as Power Amplifiers (PA), WiFi/BT, and Memory components to isolate internal circuits from external interference. As shown in Figure 7, it helps maintain signal integrity and system stability.
**Figure 7: Conformal Shielding Structure in WiFi Module**
For complex SiP packages that integrate multiple subsystems like AP/BB, Memory, WiFi/BT, and FEM, internal interference becomes a significant challenge. Conformal shielding not only isolates the package from the outside but also separates internal subsystems to prevent cross-talk. In large SiP packages, electromagnetic resonance can occur due to the wide noise bandwidth of digital systems, leading to instability. Compartment shielding divides the shield into smaller cavities, raising the resonant frequency and reducing interference.
A typical example is the S1 SiP package in the Apple Watch, as shown in Figure 8.
**Figure 8: Compartment Shielding in Apple S1 SiP Package**
**Summary of Advantages of SiP Conformal Shielding**
- Flexible and adaptable to different designs
- Minimizes stray EMI emissions within the package
- Reduces interference between adjacent components
- Has minimal impact on package size and weight
- Lowers processing and assembly costs
- Saves PCB and internal device space
- Provides excellent electromagnetic shielding performance
- Can replace bulky metal shields
Conformal shielding is a game-changer for SiP technology, enabling smaller, more efficient, and more reliable devices. It’s well-suited for the future of mobile and wearable electronics.
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