A shielding cover is an alloy metal enclosure, a critical component for reducing monitor radiation. When applied to MID or VR devices, it effectively mitigates mutual interference between internal modules. It is commonly used for isolation among the main control module, power supply module and Wi-Fi module.

Figure 1: Use of shielding case
01 Shielding cover clip

Generally, products that utilize wireless communication often incorporate a shielding frame on the circuit board to isolate electromagnetic interference (EMI). However, for the shielding frame to function effectively, it typically requires two components: one is the shielding frame using surface-mount technology (SMT) components, and the other is a shielding cover. This necessitates the creation of at least two sets of press molds.

Nowadays, some quick-thinking manufacturers have come up with a method using clips to replace shielding frames. These clips can not only be assembled using SMT, but also have a small size, so they are not afraid of deformation. These clips can directly replace shielding frames. After the clips are soldered to the circuit board, the shielding cover can be directly installed between these clips and clamped, which is equivalent to saving the cost of a shielding frame.

Figure 2：Common shielding case clips

Although shielding clamps have numerous advantages and cost benefits, there are still many engineering design issues that need attention:

1. Is there any suggestion on how far apart should clips be placed? According to the manufacturer's response, generally placing a clip every 25mm is sufficient.

2. Basically, we have designed and placed a shielding clip at the corners, which makes it easier for operators to align accurately when installing the shielding cover. Additionally, we have designed some grounding wires in other areas without shielding clips. On one hand, this can slightly enhance the electromagnetic isolation capability of the shielding cover. On the other hand, if the shielding clip becomes ineffective, it can be quickly replaced with a shielding frame without the need to redesign the circuit board.

02 Module for using shielding case

In the PCB design of MID or VR products, we often shield certain modules

1. Power module (PMU+DCDC+LDO)

As shown in the figure, the power module, typically acting as a heat source and interference source on the PCB, can effectively reduce its external radiation interference by simply adding a shielding case.

Figure 3：Shielding cover of power module

2. Core module (CPU+DDR+Flash[EMMC])

As the core component of a PCB, the stable and undisturbed operation of the core module is a crucial part of system stability. Being a module susceptible to external interference, it is usually designed with a shielding case for protection, as shown in the figure.

3. Wifi and Bluetooth modules

With the increasing integration of modules, WiFi modules also incorporate many other functions, such as Bluetooth. The more integration, naturally, the more interference it will cause to the reception of WiFi signals. Another major source of interference is the components on the PCB board. Their high-frequency circuits produce strong interference when they operate. At this time, brand manufacturers mostly adopt shielding measures to remove or reduce the interference from the motherboard to the antenna. A metal shield is a good choice, as it can effectively shield electromagnetic waves from affecting the internal circuits, while also blocking the internal electromagnetic waves from radiating outward. Of course, the location of the antenna is also crucial. It is generally placed in a relatively clean area near the board edge. As shown in the figure, a WiFi Bluetooth module with a shield is demonstrated.

Figure 4: Shielding Cover for Wifi and Bluetooth Module

When designing the shielding case, it is recommended to use a rectangular shape to avoid the complexity of polygonal shapes, which can increase production difficulty. As shown in the figure, it demonstrates common drawing methods and the placement of shielding case clips