Posts Tagged ‘high quality pcb’

Ten-Layer High Density Interconnect Board from Rush PCB Inc.

Written by Admin on . Posted in PCB, PCB Assembly and component, PCB Manufacturing

The advent of revolutionary new products, driven by miniaturization of components and semiconductor packages supporting advanced features, is driving the Printed Circuit Board (PCB) industry to increase the functionality of their boards within the same or reduced areas. This includes products such as the hand-held touch-screen computers, 4G network communications, and industrial and military applications such as smart ammunitions and avionics. Eminent PCB manufacturers such as Rush PCB Inc. are providing solutions for the above with High Density Interconnect (HDI) boards.

HDI PCBs use high performance thin materials as prepregs, have fine copper lines, and use the Every Layer Interconnect (ELIC) technology to offer very thin flexible PCBs with very high functional density per unit area. Advanced HDI PCBs make use of multiple layers of copper filled stacked in-pad micro-vias that enable interconnections with even greater complexity.

Rush PCB Inc. is currently building a 10-layer board with an FR4 grade prepreg (TUC-872SLKSP), starting with all layers of 1/3 oz. copper. The outermost layers of copper will be coated with Electroless Nickel Immersion Gold (ENIG), and covered with a coverlay (green mask) of thickness 0.0249” ± 0.003”. Component placement will be aided by a printed white silk screen, while the width and spacing of copper traces in each layer has been carefully calculated to give precise control on the impedance. The board has an overall size of 6.857” x 5.287” and its model number is 104-032-01 Rev 10. Rush PCB Inc. will be manufacturing 100 Numbers of this HDI PCB with a lead-time of 9 days.

Stack-Up Design

Before finalizing the design of multi-layer PCB circuit boards, designers need to confirm the structure of the circuit board primarily based on the scale, physical size, and the requirements of electromagnetic compatibility (EMC). Considering the above, designers at Rush PCB Inc. have decided to use 10 layers of circuit boards. This also decided the placement of the inner layer and the manner of distribution of different signals in these layers—the stack-up design of the multi-layer PCB. This careful planning and rational selection of the stack-up design beforehand will be saving the user a huge effort in wiring and production later.

Two major factors need to be decided once the designers have determined the number of circuit board layers. These are the distribution of the special signal layers and the distribution of the power and ground layers. However, with multi-layer circuit boards such as the 104-032-01 Rev 10, designers at Rush PCB Inc. followed some general principles to obtain the best combination of signal, ground, and power layers:

  1. The signal layer was kept next to an internal power or ground layer, shielded by the copper film of the internal power layer.
  2. To keep a tight control over the impedance, the internal power layer was integrated tightly with the ground layer, so that the thickness of the prepreg between the internal power and ground layers was kept thin, of the order of 2.00 Mils.
  3. To minimize crosstalk, no two signal layers were kept adjacent each other. As far as possible, the designers placed a ground layer in between two signal layers to avoid crosstalk.
  4. To control the ground impedance, designers placed multiple grounded internal power layers.
  5. The layer structure was designed to be symmetrical.

The final stack-up is shown in Fig.1. The overall PCB thickness is only 27.20 Mils or 0.69 mm.

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Every Layer Interconnect Technology

To achieve very high-density interconnection, designers at Rush PCB Inc. have used the Every Layer Interconnect (ELIC) technology. This is a method where each layer has its own copper filled laser-drilled micro-vias. When stacked up, it provides the opportunity for dynamic connections between any two layers in the PCB. Not only does this offer an increased level of flexibility but also maximizes the circuit density. The designers took up the additional complex challenges in routing with Via-In-Pad (VIP) and employing blind and buried vias. Laser drills were used for drilling the via holes, and they were filled up with conductive copper paste.

PCB 104-032-01 Rev 10 uses a total of 32 sets of blind and buried vias between the following layers, as shown in Fig.2:

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Impedance Control

Designers at Rush PCB Inc. have referenced the signals on the top and bottom layer to the ground plane next to them. Likewise, signals on other layers are referenced to ground planes adjacent to them. High-speed signal routing on an inner layer is sandwiched between ground and power planes. Careful design of trace width, spacing, and prepreg thickness has led to a tight control over single-ended and differential impedance as shown by calculations in Fig.3, Fig.4, Fig.5, Fig.6, and Fig.7:

Fig.3

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PCBs – High Quality Design

Written by Admin on . Posted in PCB Design

pcb manufacture board

 

 

Almost every electronic item around you consists of one or more Printed Circuit Boards (PCBs). PCBs hold components and also provide connections between these components.

So, if you’re an Electrical or Electronics engineer, the chances are that you will design PCBs at some stage in your career. Despite this design being a key function of electrical engineering, it’s not something that is widely taught in engineering programs. It’s not difficult for engineers to understand the core functions required for effective PCB design. There are a lot of elements to consider. All functional requirements must be met including schematic designs, component placement, and routing. Other factors that need to be considered include the schedule and cost.

Create a Schematic Diagram

Converting the concept of requirements into a PCB will require electronic language and logic. Start with a schematic diagram. The schematic diagram will include the overall design and the interconnections between circuits and components, identify the component placement, and address other factors such as the PCB material and temperature requirements.

Generate a Bill of Materials

The Bill of Materials (BOM) should be generated in conjunction with the schematic diagram. It is a summary of all the components and links required for production of the PCB. There are five key aspects of the BOM:

  1. The number and type of each component.
  2. The identification of a component in a circuit on a PCB.
  3. The numeric value of ohms, farads, etc.
  4. The footprint of each component on the PCB, and if available
  5. The manufacturer’s part number.

Placement on the PCB

Each component will need to be located based on function, thermal management and electronic noise. The order of placement is:

  1. Connectors,
  2. Power circuits,
  3. Sensitive and precision circuits,
  4. Critical circuit components,
  5. Everything else.

Following the initial placement, the PCB should be tested and reviewed, with adjustments made based on power tolerance and budget.

Routing

All PCB components are interconnected through routed traces. Elements that should be considered in routing include power levels, noise sensitivity (or generation) and routing capability. As a guide, traces with a width of 10 to 20mils can carry the current of 10 to 20mA and 5 to 8mils of carrying current lower than 10mA. If there is a requirement for high-frequency or rapidly changing signals, designers should consider routing using high-frequency nodes.

Thermal Management

Heat is a crucial factor in design. An ideal design will keep the entire board at a uniform temperature during operation. Thecomponents and links with different thermal activity need to be balanced in the design. Factors to consider include copper thickness, the number of layers and the board size.

Three ways of addressing heat include ensuring solid ground or power planes with more layers that are connected directly to heat sources; ensuring the heat transfer is optimized by developing effective heat and high-current routes; and by maximizing the area used for heat transfer.

Completing a Final Check

A final check of the design will include Design Rule Checking (DRC). DRC will determine whether the physical layout of the PCB meets Design Rules (a series of recommended parameters). This is a major step during signoff on the design, and includes validating Layout Versus Schematic (LVS), XOR, Electrical Rule Checks (ERC) and Antenna Checks.