PCB Design Requirement for Smartphones

Up to now, smart phones have become such a must-have electronic product that more than one third of daily communications and activities are completed through smart phones with their value rapidly rising every year. It's estimated that mobile phones featuring language will be decreased as a rate of 23.5% by 2020. Contrarily, smart phones at all levels will maintain a growth trend of 8.0% by 2020, including low-cost and low-functioning smart phones, medium smart phones and high-end smart phones.

Apart from ordinary functions like voice communication and emailing, smart phones today should conform to functions that are equivalent to PCs' including webpage browsing, online communication and service and social media etc. Furthermore, the latest operation system allows smart phone users to easily download windows with particular functions and multi-media self-customized software and smart phones today are even capable of connecting with smart watches, PCs, home appliances and on-board equipment to meet more demands of people. When it comes to appearance and dimensions, smart phones will develop towards large scale but thinness. In the future, smart phones with thickness less than 8mm will become a main stream. Monitors move to high definition (HD) and large screen. The equipped camera will be upgraded from 16-million pixels to 20-million pixels. Besides the expected modifications introduced above, other specification modifications of smart phones are summarized into table below.

Item 2014 2018 2024
Average external dimensions(W×L×H/mm) 77.5*152.8*8.5 75*150*8.0 70*145*7.0
Average volume (cm3)/weight(g) 100/171 90/160 71/150
Power consumption in calling(W) 0.6-1.2 0.5-0.9 0.4-0.6
Monitor Display device LCD, OLED LCD, OLED, Flex LCD,
Color electronic paper
LCD, OLED, flex LCD,
Color electronic paper,
Spontaneous emission components
Dimensions (in) 4.95-6.0 5.7-7.0 5.0-7.5
Definition Wide-VGA-Wide-XGA
High-Definition TV(1080P)
Full High-Definition TV(4K)
Full High-Definition TV(8K)
Camera Mode CMOS
Resolution (million) 8-20 8-24 8-40
Near Field Communication Infrared communication, Bluetooth,
NFC, wireless LAN, WiMAX
Bluetooth, NFC, Wireless LAN,
WiMAX, millimeter wave
Master Record Device Internal storage,
Memory card web server
Internal storage,
Memory card cloud server
Battery Lithium-ion battery, Li-polymer battery Lithium-ion battery, Li-polymer
battery, Solar cell, Fuel cell

Smart Phone PCB Requirement

Based on functions and development trend of future smart phones, highly multi-layer printed circuit boards should be applied as mother board and low multi-layer PCBs as complementary daughter board. When it comes to the fabrication of mother boards, 10-layer build-up multilayer (BUM) PCBs are usually selected. Owing to function integration led by semiconductor packaging (SiP), it's extremely likely that layer count will maintain unchanged or even reduced. Since the year of 2015 witnessed the application of 64-bit processor and IC pin spacing has been shrinked from 0.4mm to 0.35mm, layer count of mother board will possibly increase to 12 layers or more for the time being. The development trend of board structure and distribution in smart phones are summarized in the following table.

Item 2014 2018 2024
PCB Count 1-3 0-3
Motherboard Type BUM PCB BUM PCB, Glass PCB
Motherboard Dimensions (mm) 50*50-55*120
Layer Count of Smartphone Motherboard PCB 8-12 8-10 6-10
Sum of Components on Smartphone Motherboard PCB 500-1300 500-1000
Min Dimension of Components (mm) 0.4*0.2
Sum of LSI 16-28 14-25 10-20
FPGA Sum 7-14 6-13 5-12
Min Spacing (mm) 0.4 0.35 0.25
Max Terminals 1044 1200
Sum of Function Modules 5-15 4-12 3-10
Sum of Connectors 5-20 4-15 3-10

Technological design of PCB is so important that it plays a key role in manufacturing PCBs effectively with low cost. A new generation of surface mount technology (SMT) requires that designers have to take manufacturing issues into consideration from the beginning due to its complexity since a little modification of design files will definitely lead to delayed production time and increased development cost. Even a change of a pad position requires rerouting and solder paste stencil remanufacturing. The situation becomes tougher for analog circuits that strive for both redesigning and retesting. Nevertheless, if issues maintain unsolved, more loss will be caused in volume production in the end. Therefore, designers must pay full attention to technological issues from the beginning. One simple rule: the earlier technological issues are solved, the more beneficial it'll be for manufacturers.

Elements that should be taken into account in terms of technological design of smart phone circuit boards include:
• Transmission line, positioning hole and fiducial marks compatible with automatic manufacturing and assembly;
• Panels associated with manufacturing efficiency;
• PCB material, PCBA method, component distribution & packaging type, pad design and soldermask design related to soldering percent of pass;
• Component spacing and test pad design connected with inspection, rework and testing;
• Silkscreen or corrosion characters associated with assembly, debugging and wiring.

Smart Phone PCB Design Requirement

a. Laminate multilayer PCB

Laminate multilayer PCB fabrication technology is a type of multilayer PCB fabrication technology that is currently being widely applied. During the application of laminate multilayer PCB fabrication technology, substractive process is applied to manufacture circuit layer. Interconnection between layers is achieved through stages of lamination, mechanical drilling, electroless copper and copper plating. Finally come solder mask, solder coating and silkscreen to complete a piece of circuit board.

b. BUM technology

On insulating substrate board or traditional double-sided or multi-layer board, coated insulating dielectric is applied to form leads and through holes through chemical copper plating and electrical copper plating. The process continues over and over again until multilayer PCB with demanded layer count is finally manufactured. The optimal feature of BUM PCB is that substrate layer is so thin, trace width and spacing so low and via diameter so small that it features so high density. Thus, it can be applied in IC-grade high-density packaging.

c. Fiducial marks

As a generally-accepted rule, each side of daughter board in smart phones should have at least 2 fiducial marks. When space is actually so limited, they can be flexibly arranged. They should be designed to be a circular graphic whose diameter is 1mm (40mil). With contrast between material color and environment, solder mask area should be left 1mm (40mil) larger than fiducial marks and no character is allowed. When real estate is so limited, size of solder mask area can be arranged to be 0.5mm wider but solder pads with the same color shouldn't be designed within a range of 3mm.

Additionally, fiducial marks on the same board should feature the same internal background, that is, they should keep compatible in copper coating. A lonely fiducial mark with no routing around should be designed to be a protective circle with an internal diameter of 3mm and circular width 1mm. Moreover, coordinate figures must be featured by fiducial marks that shouldn't be regarded as a sign after PCB design.

d. Panel Design

Double-side v-groove panel method works well for square PCBs with attributes of neat margins after breaking up and low manufacturing cost. Thus, it is firstly suggested. Generally, an angle of 30 degrees is applied with its thickness to be one fourth or third of board thickness. However, this method doesn't fit for printed circuit boards with ICs with BGA or QFN packages.

Long-slot hole plus circular hole must be applied in mother boards with more than 4 layers while other daughter boards such as button board, LCD board, SIM card board and TF card board should select panel method based on the figure and shape of printed circuit boards. It's suggested that long-slot hole plus circular hole should be applied to arc or irregular shapes. Our article of The Surprising Secret to Designing Combination Method of PCB Panels will tell you more combination methods in terms of panel design.

As people's must-have devices, smartphones are developing towards intelligentization, miniaturization and multi-functions, thereafter requiring higher demands for PCBs that conform to all the functions of electronic devices. If you need a reliable PCB production partner to manufacture your smartphone PCBs, PCBCart can help. We have been providing quality guarantee full PCB production services for companies from telecommunications fields for 10 years. Our experience and experts allow you to get the best ever circuit boards at cost effective price.

Require bare board PCB fabrication and assembly service for telecommunication devices? Get your PCB price using our PCB quote system, it is super easy and totally FREE! Shall you have any questions on how PCBCart manufacture smartphone PCBs or electronic boards for other telecommunication applications? Contact our experts at anytime!

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Helpful Resources:
How to Design High-Quality PCBs
The Key PCB Design Rules You Have to Know
Commonly Seen PCB Design Issues
Possible Problems and Solutions in the Process of PCB Design
Full Feature PCB Manufacturing Service from PCBCart - Multiple Value-added options
Advanced PCB Assembly Service from PCBCart - Start from 1 piece

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