**Foreword**
Mobile devices are continuously evolving toward being lighter, thinner, and more compact. The mobile phone industry has followed this trend closely. This can be observed through the size changes of several generations of iPhones—each new model is thinner than the last (Figure 1). With the rise of the Internet of Things (IoT) and wearable technology, this miniaturization trend has reached its peak.
**Figure 1: iPhone thickness changes over time**
The thinning of smartphones has been made possible by advances in various technologies, such as System-in-Package (SiP), PCB design, and display innovations. One of the key enablers is EMI shielding technology. Traditionally, mobile phones used metal shielding covers to block electromagnetic interference. However, these covers take up valuable space on the PCB and inside the device, limiting further miniaturization.
A newer approach, known as **conformal shielding**, integrates the shield directly into the package. This eliminates the need for an external shield, saving both space and cost. As shown in Figure 2, most of the components on the iPhone 7, including WiFi/BT, Power Amplifiers (PA), and Memory modules, utilize conformal shielding. This allows for high integration, reduced size, and improved performance.
**Figure 2: Modules with conformal shielding on the iPhone 7 motherboard**
**Conformal Shielding in SiP Packages**
Shielding in electronic systems serves two main purposes: compliance with EMC regulations and preventing signal interference. Traditional shielding methods involve placing a metal cover on the PCB, which can complicate mass production and reduce repairability. In SiP packages, similar approaches like overmolded shielding have been used, but they often increase the module height and introduce additional manufacturing costs.
**Figure 3: Traditional shielding vs. overmolded shielding in SiP packages**
Conformal shielding offers a better solution. As seen in Figure 4, it conforms to the shape of the package without adding extra volume. This makes it ideal for ultra-thin and compact designs.
**Figure 4: Conformal shielded SiP package vs. traditional shielding**
**Performance of Conformal Shielding**
Conformal shielding delivers excellent electromagnetic shielding performance. It can achieve up to 12 GHz in far-field and 6 GHz in near-field, with shielding effectiveness above 30 dB in the 10 MHz to 100 MHz range. As shown in Figure 5, actual test results confirm its effectiveness.
**Figure 5: Test results of conformal shielding**
**Process of Conformal Shielding**
There are currently three main processes for conformal shielding: electroplating, spraying, and sputtering. Each has its own advantages and disadvantages. For example, sputtering provides a uniform and thin layer, making it ideal for high-frequency applications. The process flow for sputtering is illustrated in Figure 6.
**Figure 6: Sputtering process for conformal shielding**
**Application of Conformal Shielding**
Conformal shielding is widely used in SiP modules such as PA, WiFi/BT, and Memory. It isolates internal circuitry from external interference. For complex SiP packages that integrate multiple subsystems like AP/BB, Memory, WiFi/BT, and FEM, internal interference becomes a major concern. Conformal shielding helps isolate these subsystems and reduces electromagnetic resonance.
In some cases, **compartment shielding** is also used. This involves dividing the shielding cavity into smaller sections, increasing the resonant frequency and reducing noise. A typical example is the S1 module in the Apple Watch, as shown in Figure 8.
**Figure 8: Compartment shielding in the Apple S1 SiP package**
**Summary of Advantages of SiP Conformal Shielding**
- Flexible and adaptable to various SiP designs
- Minimizes stray emissions and EMI within the package
- Reduces interference between adjacent components
- Has minimal impact on package size and weight
- Lowers costs associated with special shielding parts
- Saves PCB space and internal equipment room
- Offers excellent EMI performance and can replace large metal shields
Conformal shielding is becoming a key technology in the evolution of SiP packages. It supports the ongoing trend of device miniaturization while maintaining high performance and reliability.
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