Keywords: Backplane Board, Backplane PCB

Containing sockets and slots to interconnect various devices or PCB assemblies in parallel to each other a backplane is an electronic system. For an electronic system, Backplane PCB acts like a Backbone and to each slot; it distributes low-voltage power.

The working of passive electronic components such as diodes, capacitors, and resistors as well as backplanes is evaluated by Backplane testing. The electrical and physical connections between system components are provided by the backplane.  It is essential that within its prescribed parameters, it is operating. Some tests are performed to ensure the smooth working of a backplane. Backplane testing is called the process of identifying the major faults in the backplane by using test processes.

Maximum voltage, test resistance, test points and maximum current are included in Key Specifications of backplane testing.

Following types of tests are present in Backplane PCB Testing:

Visual Inspection: For correct placement, components on the backplane are checked individually in this test. Checking component orientation and solder joints are included. It can be done through Automated Optical Inspection (AOI) or manually.

Electrical Tests: By sending an electrical current through the traces and pins on the board, these test checks the connections. Two major areas to test are:

• To ensure that there is no connection, Short or Isolation which means there is a space between the pins.
• Open circuit or Continuity which means there is a connection between the pins.

In two terms, the electrical test provides confirmation.  If a connection exists between the test points, it is Continuity and if doesn’t, it is Short. Since a connection which is not required can cause interference on the board and lead to malfunctions, this test is essential.

Signal Integrity Analysis and Simulation: As within the backplanes, higher speed signals are constituted. For the frequency domain and time domain measurements, network analyzers are used to analyze such signals.

Functional Test: For checking how the circuitry will work after integrating with the application or intended final device, this test is done.

Key Tips and Difficulties for Backplane PCB Fabrication

For carrying function boards including line cards or daughter boards Backplane PCB, also known motherboard, is a type of baseboard responsible. Carrying daughter boards and distributing power to function boards is the major task of backplane board so that signal transmission and electrical connection can be achieved. Therefore through the cooperation between its daughterboard and backplane, the system function can be acquired.

The backplane board functions gradually cover power distribution, signal transmission and function board carrying as IC component features increasingly higher integrity. Together with rapid progress that is made in electronic assembly, the development of high-speed digitalization and high frequency of signal transmission, the I/O count keeps rising. Backplane boards have to reach higher requirement to implement those functions in terms of signal transmission quality, board thickness, layer count, reliability, via count and frequency.

Accordingly, Backplane PCB fabrication have to be confronted with rigorous challenge on stub, board size, board thickness, alignment control, layer count and back drilling depth to obtain such high requirement in performance. In other words as far as backplane fabrication is concerned, all the mentioned aspects are definitely key issues. To display the key difficulties met in backplane PCB fabrication process, this article aims and based on PCB, here you can discuss some handy tips.

1. Backplane Boards Drilling Technology

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

Tips

• Through the application of depth control in a conductive way, Drilling depth can be accurately determined.
• Based on the hole drilled through X-ray drilling, CCD method should be applied in drilling CCD marker and backplane board.

2. Alignment Control

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

Numerous procedures and elements affects alignment control among which layer stack-up most matters. Three types of compositions are present usually in Multi-layer PCBs: thermocouple heating, pin-lam and mass-lam.

Tips

• Pins category choice used is extremely crucial as pin-lam stack-up is used. For example, we find that compatible with the requirement on alignment control, four pins are used to perform better than eight circular pins.
• Copper-iron rivets plus short dowels will be a good selection when pin-lam can’t be applied due to some limitations.
• In pin-lam, the optimal composition method lies as it won’t arouse shock effect on core board.

3. ICD Analysis

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

Tips

• To certify that gel residue has been eliminated, drilling parameter control should be optimized.
• To stop resin due to insufficient aging being left on inner copper layers, Board material aging extent should be analyzed.

4. Electroplating Capability

The aspect ratio will be high as well Due to high thickness of backplane board. For ensuring sufficient copper at hole, sufficient copper will be inside hole if the electroplating is not deep enough. Aperture is affected, incompatible copper thickness at hole wall and leading via aperture is resulted if too much copper will be left at hole mouth.

Tips

• New DC plating solution must be used.
• With DC plating solution, Pulse plating solution should be compared in terms of solution stability, reliability and plating capability.

5. Back drilling Stub

Stub will lead to even signal transmission failure or signal to be distorted as far as high-speed signal transmission is concerned. Therefore, stub on high-speed signal transmission should be clarified the negative effect caused by. When the length of stub is less than 0.25mm, its effect on signal is can be ignored and quite low up to now. Within 0.25mm, stub length should be controlled as a result in Backplane PCB.

Tip:

To minimize its effect on signal transmission quality, Stub length should be controlled within 0.25mm.