How to deal with the "big" challenge of 5G PCB?

10.3 billion, 8.5 billion. Isn't that scary to see? In fact, it is the number of transistors of Huawei Kirin 990 5G chip and Apple A13 Bionic chip respectively. The manufacturing process is higher, the number of transistors is more, and the CPU frequency is higher, which means the chip has higher performance and carries more rich functions. With the arrival of the 5G era, chip manufacturers represented by Huawei Hisse, Apple Samsung and Qualcomm Mediatek have launched their own flagship chips. Not long ago, Qualcomm's Snapdragon 865 platform was also officially released. In 2020, there will be a wave of phones with 5G chips, and both chip and phone manufacturers have "accepted" the 5G challenge.

For electronics manufacturers, how to deal with the 5G challenge?

Challenges for 5G

PCB stacking challenge

The components are placed on the PCB board in reasonable rules, which is called PCB stacking. PCB stacking needs to consider the area of PCB board, smooth layout routing, RF performance, PCB heat dissipation, structural performance, weight of the whole machine, etc. The following picture shows a circuit board inside a 5G flagship mobile phone with densely packed components.

5G era requires high speed, higher requirements for functions, wired charging, wireless charging, reverse charging, 4 cameras, screen fingerprint, large capacity battery, NFC, higher refresh rate screen, good experience, means more functional circuits, inch of land in the mobile phone PCB, how to put down so many components, will be a severe challenge?

5G mobile phone PCB

PCB heat dissipation challenge

4G network delay is around 40~60ms, 5G network delay is expected to reach 1ms, lower network delay means more enjoyable game experience, 5G era will no longer appear "460ms" to play games.

We all know that playing games or watching TV series for a long time will heat up mobile phones, because the CPU will generate heat when running at a high speed. In addition, we will find different mobile phones have inconsistent heating performance, some mobile phones concentrate on the top and some mobile phones concentrate on the back, which is because of different PCB schemes, the heat transferred to the mobile phone case is not uniform. 5G era, how to better deal with heat sources, how to effectively add heat dissipation materials, will also be a serious challenge?

Comparison of infrared thermal image of a mobile phone

PCB antenna challenge

Huawei Mate30 series phones are built with 21 antennae, of which 14 are for 5G (the other 7 are for WiFi, BT, GPS and NFC). The standard 5G is actually 8 antennae, and the standard 4G is 2 antennae, which is 3x. More antennas mean better RF performance, antenna area, antenna placement, antenna radiation, MIMO (multiple input/output) technology application, will also be a serious challenge?

Cope with challenges

1. Guoju launches ultra-small packaging resistance

Yageo's RC0075 and RC0100 resistors are the smallest package resistors at present. As the most used electronic components in electronic products, 800~1000 multilayer ceramic capacitors are used inside a high-end mobile phone, and the number of resistors is slightly less than that of capacitors. The resistance and capacitance of a smaller package will save more PCB space. To cram in more "user experience."

Under such a small package as RC0075, the maximum operating voltage can reach 10V. Among many electronic products powered by lithium-ion batteries (3.8V~4.2V) (including mobile phones), 10V is already a high enough voltage, and 0075 package resistance can be boldly chosen.

The power, working temperature and working voltage comparison table of Yageo patch resistor. Knowing these parameters, do you still worry about how to select the resistance?

2. KEMET T540/T541 series tantalum capacitors have very low ESR

As we all know, mobile phones will generate large ripple current during phone calls or data communication. Tantalum capacitors with high ESR, U=ESR*I (I is ripple current, U is ripple voltage), will generate higher ripple voltage. High ripple voltage will lead to a risk. It pulls the battery voltage even lower, shutting down the phone.

The KEMET T540/T541 series tantalum capacitors have an extremely low ESR, allowing a larger ripple current to pass through. The high capacitance of the T540/T541 series also plays a crucial role in ripple voltage.

Another important feature of T540/T541 series is its high frequency retention ability. As shown in the figure below, the capacitance value of the T541 series capacitor is almost constant at a frequency lower than 100K. The impedance curve at high frequency presents approximately ideal capacitor characteristics, and the influence of ESR and ESL is very low.

3. TDK launched NTC with small thermal temperature coefficient

NTC thermistor is a kind of temperature sensor, because the circuit is simple, at least two devices, the cost is cheap, is widely used. The Xiaomi 10 series 5G mobile phone released in February has 9 built-in temperature sensors, which can accurately monitor the temperature of each key point on the PCB, and then accurately control the temperature. It is highly likely that NTC will be used as the temperature sensor, and less circuit components will be used, which will greatly reduce the PCB space and BOM cost.

TDK introduced the thermal temperature coefficient NTC thermistor. The thermal temperature coefficient refers to the time required for the thermistor body temperature to change by 63.2% of the difference between start and end temperature when the temperature changes abruptly under the condition of zero power. Generally speaking, it is the sensitivity of NTC thermistor to detect temperature.

The low temperature coefficient of TDK's NTC thermistor can quickly monitor the temperature of 5G PCB board, contributing to the challenge of 5G PCB heat dissipation.

NTC thermistor temperature measuring circuit

The most basic is often the most difficult to break through, but in the face of 5G, PCB should break the bottleneck, resistance and tolerance components such as "small" is an inevitable trend.