Keywords: Backplane Board, Backplane PCB

Backplane

In a wide sense, a type of PCB (Printed Circuit Board) is also a Backplane PCB. Carrying line cards or daughter boards, a backplane is a type of motherboard to achieve custom functions. Carrying boards and distributing functions including power signals, supplies, etc. to each daughterboard is the leading function of the backplane so that appropriate signal transmission and electrical connection can be obtained. Backplane, Working together with carried boards, is capable of leading the whole system to run smoothly and logically.

Backplane Attributes

With a nature of specialization, Backplane has been a type of product when it comes to the PCB fab industry. Therefore, as compared to ordinary PCBs, the backplane holds more specializations.

• Heavier

It’s not difficult to understand high weight is the result of thicker boards. Besides, the weight of the backplane also includes a high volume of copper.

• Thicker

The backplane is expected to transmit signals at a high speed and usually features more layers. The copper layer should be thick enough when application cards are inserted into the backplane with high consumption, to provide the necessary current. The Backplane Board becomes thicker than ordinary PCBs as a result of all the elements mentioned.

• High Drilling Hole Count

The backplane has to realize more signal transmissions and electrical connections because of function implementation and complex structure. On a large number of buried or blind vias, both of them depend. To contribute to function achievement, the backplane has to carry more drilling vias or holes as a result.

• High Heat Capacity

The backplane thereafter features higher heat capacity as the backplane is thicker and heavier as compared to ordinary PCBs.

Backplane Fabrication

Backplanes should be manufactured with special technology and attention owing to the higher requirements and complexity of backplanes.

• Cleaning

It usually occurs that working fluid feature more drilling holes or vias than ordinary circuit boards and flows out as backplanes are thicker. Therefore, to stop working fluid from staying in drilling vias or holes, it’s extremely important to clean drilling holes with a high-pressure cleaning machine.

• Reflow Soldering

Since heat on backplanes is more difficult to be dissipated from the board as compared to ordinary boards, backplanes are heavier and thicker. After reflow soldering, it takes backplanes more time to cool down In other words. To provide more time for backplane boards to be cooled down, the reflow soldering oven should be strengthened as a result. In addition, at the exit of the reflow soldering oven, air cooling should be forced to be used to make backplane boards cool down.

• Component Assembly

For the concern of reliability, passive components tend to be placed on backplanes traditionally. However, on backplanes to lead active boards, active components such as BGAs (Ball Grid Arrays) have been increasingly designed to maintain at a fixed cost. Component assemblers should be able to place silicon-packaged components and resistors and smaller capacitors. Additionally, larger assembly platforms are called for the large size of backplanes.

• Layer Alignment

Layer alignment is therefore very difficult to obtain as of the drilling hole count and higher layer count. During the process of backplane board fabrication, layer alignment should be done with much high technology and care accordingly.

• Backplane Development Trend

The backplane should develop towards high thickness, large dimension, and ultra more layers, playing a role of a key node in terms of network transmission as data transmission and network communication move toward mass-volume and high-speed transmission. All in all, huge challenges to PCB manufacturers in the future will be brought about by all the above expectations.

Backplane PCB Fabrication Difficulties

• Alignment Control

As far as ultra-multi-layer PCB fabrication is concerned, Alignment control is the foremost manufacturing difficulty since bad alignment control will lead to shorts possibly.

Among which layer stack-up most matters, Alignment control is affected by numerous elements and procedures. Multi-layer PCBs usually have three types of compositions: thermocouple heating, pin-lam, and mass-lam.

Tips:

Since it won’t arouse a shock effect on the core board, the optimal composition method lies in pin-lam.

Copper-iron rivets plus short dowels will be a good selection when pin-lam can’t be applied due to some limitations.

The category of pins used is extremely significant as pin-lam stack-up is used. For example, to perform better than eight circular pins, we find that four pins are used compatible with the requirement of alignment control.

• Drilling Technology

Drilling is possibly too short to reach the board Due to the high thickness of the backplane board. However, too long drilling tool suffers from breaking during the drilling process. Dramatically reducing backplane PCB performance, the burr may be caused and too much dust may block the hole In addition.

Tips:

Through the application of depth control in a conductive way, Drilling depth can be determined accurately.

CCD marker depends on the hole drilled through X-ray drilling and the CCD method should be applied in drilling backplane board.

• Electroplating Capability

The aspect ratio will be high as well due to the high thickness of the backplane board. Affecting the copper thickness at the hole wall to be incompatible, leading via aperture and aperture, sufficient copper will be inside the hole while too much copper will be left at the hole mouth to make sure sufficient copper at the hole if the electroplating cannot be deep enough.

Tips

New DC plating solutions such as EP should be used.

In terms of plating solution, reliability, capability, and stability, the Pulse plating solution should be compared with the DC plating solution.

• ICD Analysis

ICD tends to be occurred during the process of high-frequency material fabrication causing dramatic quality risk to long-term electrical connection and reliability. So that the ICD cause and its solution must be summarized such issues can be avoided in the process of backplane PCB manufacturing. The cause of the ICD issue lies in the insufficient cleaning carried out and resin gel residue left on the inner copper layer.

Tips:

To certify that gel residue has been eliminated, drilling parameter control should be optimized.

Due to insufficient aging being left on inner copper layers, the Board material aging extent should be analyzed to stop resin.

• Back drilling Stub

The stub will lead signal transmission failure or even the signal to be distorted as far as high-speed signal transmission is concerned. Therefore, the negative effect due to stubs on high-speed signal transmission must be clarified. Up to now, it can be summarized that its effect on signal is quite low and can be ignored when the length of the stub is less than 0.25mm. Within 0.25mm, stub length should be controlled as a result. Backplane PCB is reliable.

Tips:

Within 0.25mm, Stub length should be controlled to reduce its impact on signal transmission quality.