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5 Aspects You Have to Know about Backplane
In a wide sense, backplane is also a type of PCB (Printed Circuit Board). Specifically speaking, backplane is a type of motherboard carrying daughterboards or line cards to achieve custom functions. The leading function of backplane is to “carry” boards and to distribute functions including power supplies, signals etc. to each daughterboard in order that appropriate electrical connection and signal transmission can be obtained. Working together with carried boards, backplane is capable of leading the whole system to logically and smoothly run.
Nowadays, IC (Integrated Circuit) component integration goes up and I/O number rises, along with the progress in terms of electronic assembly technology and high frequency of signal transmission and high speed of digitalization. In addition, electronic devices call for upgrading on high-speed development. As a result, backplane should carry functions like functional daughterboard carrying, signal transmission and power supply transmission. Meanwhile, the attributes of backplane should be specific and obvious, which should be displayed in the following aspects: layer count, thickness, via count, high reliability demand, high frequency, signal transmission quality at a high speed etc.
Attributes of Backplane
Backplane has been a type of product with a nature of specialization when it comes to PCB fab industry. Therefore, backplane holds more specializations than ordinary PCBs.
Backplane usually features more layers and it is expected to transmit signals at a high speed. When application cards with high consumption are inserted into backplane, copper layer should be thick enough so as to provide necessary current. All the elements mentioned all lead backplane to be thicker than ordinary PCBs.
It’s not difficult to understand that thicker boards will definitely lead to high weight. Besides, a high volume of copper also adds to the weight of backplane.
•Higher Heat Capacity
Because backplane is thicker and heavier than ordinary PCBs, backplane thereafter features higher heat capacity.
•Higher Drilling Hole Count
Due to complex structure and function implementation, backplane has to realize more electrical connections and signal transmissions both of which depend on a large number of blind/buried vias. As a result, backplane has to carry more drilling holes or vias in order to contribute to function achievement.
Backplane Fabrication Focus
Owing to higher complexity and requirement of backplane, backplanes should be manufactured with special attention and technology.
Since backplanes are thicker and heavier than ordinary boards, heat on backplanes is more difficult to be dissipated from board. In other words, it takes backplanes more time to cool down after reflow soldering. As a result, reflow soldering oven should be strengthened in order to provide more time to backplane boards to be cooled down. In addition, air cooling should be forced to be used at the exit of reflow soldering oven to make backplane boards cooled down.
Because backplanes are thicker and feature more drilling holes or vias than ordinary circuit boards, it usually occurs that working fluid flows out. Therefore, it’s extremely important to clean drilling holes with high-pressure cleaning machine in order to stop working fluid from staying in drilling holes or vias.
Because of higher layer count and drilling hole count, layer alignment is therefore very difficult to obtain. Accordingly, layer alignment should be done with much carefulness and high technology during the process of backplane board fabrication.
Traditionally, passive components tend to be placed on backplanes for the concern of reliability. However, active components such as BGAs (Ball Grid Arrays) have been increasingly designed on backplanes to lead active boards to maintain at a fixed cost. Component assemblers should be able to place smaller capacitors and resistors and silicon-packaged components. Additionally, the large size of backplanes calls for larger assembly platforms.
Development Trend of Backplane
As network communication and data transmission move toward high-speed and mass-volume transmission, backplane should develop towards large dimension, ultra more layers and high thickness, playing a role of key node in terms of network transmission. As a result, backplanes will be fabricated with more difficulties and more requirement has to be laid to backplane board manufacturing such as backplane thickness, backplane size, backplane layer count, backplane alignment, back drilling depth and stub, electroplating drilling depth etc. All in all, all the above expectations will bring forward huge challenges to PCB manufacturers in the future.