Printed Circuit Board Glossary

Copper to Edge Clearance

Any copper, whether it is ground plane, traces or pads should not be right to the edge of the board as this will cause the solder-mask to flake and peel off after it gets routed.

Copper Etching

After the PCBs are plated, they are put through the Ammonia ETCHING machine. All the copper areas that were not plated are etched out i.e. the copper surfaces that were under the exposed/hardened film is removed.

Carbon Screening

Carbon screening involves screening a layer of conductive carbon filled polymer paste onto the board. Carbon Screening is usually used as an insulator, such as keypads for cellular phones.


This stage is for Non-Plating Through Holes (drilling holes that do not need plating), Slots, and Routing.


After the boards have been laminated with film and exposed, they are sent for electroplating of the tracks and pads. About 1 ounce of copper is deposited during the plating processes.

Hot Air Solder Levelling (HASL )

Used for SMOBC – applies, levels, smoothes and shines tin/lead solder over SMOBC. HASL allows for a stronger, shinier and cleaner Surface Finish for the circuitry.


After the PTH stage, the board is laminated with dry film and an image of the PCB design will be printed onto the board with UV lighting (exposing the film).

Laser Direct Imaging (LDI)

An imaging process which only uses a computer-controlled, highly focused, laser beam to directly define the circuit pattern onto the board.

Liquid Photographic Imageable (LPISM)

LPI is a type of solder mask that has a very high-resolution capability, allowing 2 mil solder dams and is best used in SMT applications and where a more transparent mask is desired.

Mask Relief

Mask Relief is the air gap between the exposed pads and the mask. This number can vary depending on mask type and circuit density.

Plating Through-Holes (PTH)

The board goes through the ELECTROLESS PLATING stage where 50 to 70 Micron Inches of copper is plated into the drilled holes of the board.

Plating Finishes

There are four different types of finishes available for the finished Circuit Boards:

a) Bare Plating
d) SMOBC (Solder Mask On Bare Copper)
e) Tin/Lead Plating- HASL

Resist Strip

The PCB’s are dunked into the Resist Strip liquid solution. Here the exposed film is dissolved and stripped removing the dry film.


Cutting out the final shape/dimensions of the board.

SMOBC (Solder-Mask Over Bare Copper) Plating

The areas of the board that are covered by solder-mask are bare copper.


The paint applied on top of a solder mask. It is used for identification of the components on the PCB. It uses the same material as a thermal mask.

Sprint Printing

The silk screen or indent can be printed on PCB directly using sprint printer.

Surface Mount Technology (SMT)

SMT components are designed to be loaded and soldered (“mounted”) on to the same side of the PCB. No holes are required (though they may still be used to connect different layers.

Semiconductor Devices

A material, typically crystalline, which allows current to flow under certain circumstances. Common semiconductors are silicon, germanium, gallium and arsenide. Semiconductors are used to make diodes, transistors and other basic "solid state" electronic components. The components are composed of various semiconductor devices, such as transistors, rectifiers, diodes, capacitors, and resistors, which affect the electrical current flow.


A device used to control current in an electric circuit by providing resistance.


An electric circuit element used to store charge temporarily, consisting in general of two metallic plates separated and insulated from each other by a dielectric. Also called condenser.


One that inducts, especially a device that functions by or introduces inductance into a circuit.


An electronic device that restricts current flow mainly to one direction.


A device, such as a diode, that converts alternating current to direct current.


A small electronic device containing a semiconductor and having at least three electrical contacts, used in a circuit as an amplifier, a detector, or a switch.


The metal (i.e. Tin/Lead) plating that goes over the copper circuits. Tin/Lead is placed on top of copper tracks and pads to protect it in the Etching process.

Solder Mask

Coloured Paste coated on top of circuitry for better durability of the PCB - Protects cu. from oxidization.

Thermal Solder-Mask

The thermal mask is best used for basic applications where through hole components are used. It provides a thicker and harder finish than LPI.

Through Hole

Through-hole components have been used for many years and are designed to be loaded on one side of a PCB and soldered on the other.

Tin Stripping

Tin/Lead solder that was plated onto the copper will need to be stripped because if solder-mask is screened over T/L, the mask will wrinkle and crack during baking.

Quick reference to PCB Industry Terms

  • HASL – Hot Air Solder Leveling
  • E-TEST – Electrical Testing
  • LPI –Liquid Photographical Imageable
  • LDI- Laser Direct Imating
  • SMT – Surface Mount Technology
  • HASL- Hot Air Solder Levelling
  • ENIG – Electroless Nickel Immersion Gold
  • FR4 SUBSTRATES – Fiberglass Rigid 4, most popular material
  • NC DRILL FILE – list of x & y coordinates defining hole locations and tool #s
  • PTH – Plating Thru-holes
  • TAB-ROUTING – boards are panelized and held together by tabs
  • INDIVIDUAL ROUTING – each board is shipped individually
  • V-SCORING – boards are easily broken from panel leaving clean edges
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