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Learn PCB Breadcumb Introduction Breadcumb Vocabulary

Vocabulary

Here is a glossary of words commonly used when discussing HDI PCBs. This will help you keep define terms and keep track of how each item impacts designing HDIs.

Layers

Layers on a board are defined by the different layers of material. This includes copper layers and core substrates. Between each copper foil is a PCB material, or dielectric, to insulate the copper layers from each other.

Cost implications

The more layers you want your board to have, the more costly the project will be. Each layer requires a certain amount of time to process, including steps like etching and plating, and require more material to be used. A large number of layers can also affect yield, which will affect price.

Lamination

Lamination is a process in which heat and pressure bonds two layers together. There are a few lamination choices.

Single-Double-Lamination

A single side lamination means there is only one layer of copper on one side of the laminate. Components will only be mounted on the side with copper.

A double side lamination means there is a layer of copper on either side of the laminate. Components can be mounted on both sides of the board.

Multi-layer lamination is used for a PCB with multiple layers. The copper layers are sandwiched between layers of laminate and outer copper layers.

Press out thickness

Press out thickness is the predetermined thickness a board needs to be after lamination.

Press Out Thickness

PCB materials

The substance between copper layers to insulate the copper layers is called dielectric material. The most common PCB material is FR4, fiberglass impregnated with resin, but a variety of other substances are used as well. A thicker amount of material will translate to higher cost since more of the material is used for each layer of the board.

Surface finishes

A surface finish is a layer of coating between the components and the bare PCB. The finish protects the board and any exposed copper from the outside environment.

Cost implications

Based on the material you choose, prices can vary. Keep in mind that though some materials cost less, they may not meet project requirements, and some are expensive and still may not be what the board needs. For this reason, the designer needs to determine which material would be the best fit for the particular product and environment the board will be in.

Solder Mask

Solder masks are layered on top of bare copper, or solder mask over bare copper (SMOBC). Areas of the copper without a surface finish will be covered with soldermask.

Microvia

A via is an electrical connection provided by a hole drilled between layers on a printed circuit board. Microvias are defined as any hole equal to or less than 150 microns in size, and are made by laser drills. The hole formed connects the layers with copper plating. The hole cannot penetrate more than a couple layers, so the vias need to be stacked on top of each other or staggered in the board. Microvias can be buried or blind.

Blind vias (pictured below) are vias that enter through the outer layer of the circuit board and end in one of the inner layers; it does not go all the way through.

Blind vias

Buried vias (pictured below) are vias that are buried between and connect layers in the inner layers of the board; they cannot

Blind vias

Buried vias

Cost implications: The smaller the hole needs to be, the more it will cost. This is due to the need for precise equipment use for drilling and plating.

Buried vias

Aspect Ratio

The aspect ratio is the thickness of the board versus the width of the via.

The ratio of size of microvias to dielectric thickness. This is important to make sure vias can be plated properly.

Apect Ratio
The aspect ratio is the thickness of the board versus the width of the via.
Ball grid array (BGA)

Ball grid array

A ball grid array is a type of surface mounting packaging used for integrated circuits. It has a grid of solder balls to conduct electrical signals and attach packages with many pins to the surface of a PCB. The solder balls melt, cool, and harden at the same rate so the connections are consistent. Some downsides of this process are that the melted solder balls are not flexible and can strain the connections.

Trace

The path of copper (in some cases, other metals) that connects parts of the board together and allows electricity to flow between components and features of the board.

Pad (also called Land)

These are small exposed copper areas, usually round, on a board to make a connection between a via and a trace, or a component. Pads can be off to the side of a component or under the component to save space, which is common when size is a concern. Pads can be through-hole pads or surface mount pads.

PAD

Through-hole pads are meant for the pins of components to go through them and to be soldered on the underside of the component. Surface mount pads are meant for components to be soldered on the same side of the board.

Through-hole pads

Drill to copper

The distance from the edge of the drilled hole to the copper feature (pad, pour, trace, etc). There should be enough space between the hole and the copper so that any via that is not exactly centered in the pad will not hit the copper.

Yield

Yield refers to the amount of boards you need to make to fill an order. This includes boards with mistakes or discrepancies that are replaced to send to the customer. If a shop makes 10 boards to fill an order of 5 boards, yield is 50%.

Annular rings

An annular ring is the area of the pad that surrounds a via. Microvias require small annular rings.

Annular-Breakout

Annular breakout

Annular breakout An annular breakout is when the via is not fully surrounded by the pad, ie. the via is drilled off-center. This can create problems with the connections of the vias to the layers.

Annular rings

Signal integrity describes the signal's nature and whether it has been affected or distorted by electrical properties. Signals can maintain signal integrity when frequencies are low, but at higher speeds, some signals will distort and bounce back, etc. Careful design to match traces and connections to the signal can prevent distortions.

Control Impedance

Electrical impedance is the opposition applied to a current moving through a circuit, which slows the current down. Signals in PCBs may need to arrive at its destination at different times in order to function properly. Controlling impedance, adding more or less resistance to a current, of certain signals to slow them down will allow them to reach the destination at the right time. Impedance can be controlled through the width of the trace, the space between signal trace and signal return path, relative dielectric coefficient of material, and the thickness of the trace.

Cost implications

Depending on what the board needs and how the signals behave, there may be a need for an increase in space for wider traces, or more spacing of components from other copper features, or similar considerations. Material usage may also change based on needs and that can increase or decrease price as well.

Turn time

The time it takes for a PCB job to be finished. Different requirements and processes will affect turntime. Sequential laminations for example, take more time because the board needs to go through the shop over and over to be drilled and laminated.