PCB Glossary : N to R

Nomenclature:
Identification symbols applied to the board by means of screen printing, inkjetting, or laser processes. See Legend.

Outer-layer:
The top and bottom sides of any type of circuit board.

Pad:
See Land.

Pattern:
The configuration of conductive and nonconductive materials on a panel or printed board. Also, the circuit configuration on related tools, drawing, and masters.

Pattern Plating:
The selective plating of a conductive pattern.

Photographic Image:
An image in a photo mask or in an emulsion that is on a film or plate.

Photoplotting:
A photographic process whereby an image is generated by a controlled light beam that directly exposes a light-sensitive material.

Photo Print:
The process of forming a circuit pattern image by hardening a photosensitive polymeric material by passing light through a photographic film.

Phototool:
A transparent film that contains the circuit pattern, which is represented by a series of lines of dots at a high resolution.

Plated Through-Hole:
A hole with plating on its walls that makes an electrical connection between conductive layers, external layers, or both of a printed board.

Platen:
A flat plate of metal within the lamination press in between which stacks are placed during pressing.

Plating Void:
The area of absence of a specific metal from a specific cross-sectional area.

Plotting:
The mechanical converting of X-Y positional information into a visual pattern such as artwork.

Prepreg:
Sheet material (e.g. glass fabric) impregnated with a resin cured to an intermediate stage (B-stage resin).

Pressing:
The process by which a combination of heat and pressure are applied to a book, thereby producing fully cured laminated sheets.

Printed Board:
The general term for completely processed printed circuit or printed wiring configurations. It includes single, double-sided, and multi-layer boards, both rigid and flexible.

Printed Circuit:
A conductive pattern that comprises printed components, printed wiring, or a combination thereof, all formed in a predetermined design and intended to be attached to a common base. (In addition, this is a generic term used to describe a printed board produced by any of a number of techniques.)

Printed Wiring Board:
A part manufactured from rigid base material upon which completely processed printed wiring has been formed.

Registration:
The degree of conformity to the position of a pattern, or a portion thereof, a hole or other feature to its intended position on a product.

Resin (Epoxy) Smear:
Resin transferred from the base material onto the surface of the conductive pattern in the wall of a drilled hole.

Resist:
Coating material used to mask or to protect selected areas of a pattern from the action of an etchant, solder, or plating. Also called soldermask or mask.

Rigid-flex:
A PCB construction combining flexible circuits and rigid multi-layers usually to provide a built-in connection or to make a three-dimension form that includes components.

Router:
A machine that cuts away portions of the laminate to form the desired shape and size of the printed board.

PCB Glossary : H to M

Hole Breakout:
A condition in which a hole is partially surrounded by the land.

Hole Pattern:
The arrangement of all holes in a printed board with respect to a reference point.

Hot Air Solder Leveling (HASL):
A method of coating exposed copper with solder by inserting a panel into a bath of molten solder then passing the panel rapidly past jets of hot air.

Imaging:
The process by which panelization data are transferred to the photoplotter, which in turn uses light to transfer a negative image circuitry pattern onto the panel.

Impedance:
The total passive opposition offered to the flow of electric current. This term is generally used to describe high-frequency circuit boards.

Inner-layers:
The internal layers of laminate and metal foil within a multi-layer board.

Insulation Resistance:
The electrical resistance of an insulating material that is determined under specific conditions between any pair of contacts, conductors, or grounding devices in various combinations.

Known Good Board (KGB):
A board or assembly that is verified to be free of defects. Also known as a Golden Board.

Laminate:
The plastic material usually reinforced by glass or paper that supports the copper cladding from which circuit traces are created.

Laminate Thickness:
Thickness of the metal-clad base material, single- or double-sided, prior to any subsequent processing.

Laminate Void:
An absence of epoxy resin in any cross-sectional area that should normally contain epoxy resin.

Land:
The portion of the conductive pattern on printed circuits designated for the mounting or attachment of components. Also called a pad.

Layup:
The process in which treated prepregs and copper foils are assembled for pressing.

Legend:
A format of lettering or symbols on the printed circuit board: e.g. part number, serial number, component locations, and patterns.

Liquid Photoimageable Soldermask (LPI):
A mask using photographic imaging techniques to control deposition.

Line:
See Conductor.

Lot:
A quantity of circuit boards that share a common design.

Major Defect:
A defect that is likely to result in failure of a unit or product by materially reducing its usability for its intended purpose.

Mask:
A material applied to enable selective etching, plating, or the application of solder to a PCB. Also called soldermask or resist.

Metal Foil:
The plane of conductive material of a printed board from which circuits are formed. Metal foil is generally copper and is provided in sheets or rolls.

Microsectioning:
The preparation of a specimen of a material, or materials, that is to be used in metallographic examination. This usually consists of cutting out a cross-section followed by encapsulation, polishing, etching, and staining.

Minor Defect:
A defect that is not likely to result in the failure of a unit of product or that does not reduce the usability for its intended purpose.

Multi-Layer Board:
Printed boards consisting of a number (four or more) of separate conducting circuit planes separated by insulating materials and bonded together into relatively thin homogeneous constructions with internal and external connections to each level of the circuitry as needed.

Pattern plating copperclad substrates proceeds as follows:

• Calculate the total plating time.

An acid copper plating bath based on the Lea Ronal PCM+ additive system deposits 0.0011" (1.10 mils, 28 microns, 0.81 oz) of high ductility copper in 1 hour at 20 ASF(Amps per Square Foot). Plating up "one ounce" of copper (i.e. plating 1 oz. of copper onto 1 square foot of board) is equivalent to plating a thickness of 0.0013" (1.3 mils or 34 microns).

Example: If you are starting with "half ounce" copperclad and want to plate up to a finished thickness of "one ounce", you will need to add .65 mils. The total plating time at 20 ASF will be:

[0.65 mils / (1.1 mils/hr.) x 60 min./hr. = 35.5 minutes = T

• Calculate the required plating current.

Convert the total area of the pattern being plated into square feet (remember both sides!) and multiply the result by 20. Some CAM packages output the area of the pattern as a percentage of the total board area (area enclosed by the board outline defined in the ECAD or CAM software), while others can calculate the total pattern area in any unit specified by the user. To normalize the plating field, it is often beneficial to add an exposed ¾" boundary around the board to increase to total plating area and suppress the formation of high potential areas at the edges of the pattern. These are referred to as "robber bars" or "thieving bars" since they "steal" some of the electric field from the circuit pattern.

Example: If you are plating a double-sided board with a total circuit area equal to 25 sqin. (robber bars included) you will need:

[25/144] x 20 = 3.5 Amps = C

• Carefully inspect the substrate for deep scratches and nicks that might impair the quality of the finished circuit.
• Format the drilling stack to minimize burr formation during drilling.
• Drill the through-holes and mounting holes, and mill/router any slot or cavity that is to be plated.
• Activate the hole-walls.
• While the ink is curing, take a few minutes to analyze the electrolyte. If you have a hull cell, this is a good time to run a test to insure that the organic components of the bath (which are very difficult to test directly) are in balance and present in the proper concentrations.
• After activation and curing, both sides of the substrate should be thoroughly cleaned to remove any trace of conductive ink from both surfaces. Any ink that is not removed will almost certainly show up in the worst possible place so take your time cleaning the board and make a good job of it!
• An abrasive pad (e.g. Scotchbrite® pad) can be used to remove ink that proves to be too stubborn for conventional cleaning, but be careful. You must be certain that you do not break the electrical contact between the conductive ink on the inside of the holes and the copper foil on the surface of the board or the holes in question will not plate properly.
• Rinse the board thoroughly in deionized water before proceeding.
• Dip the board into a 10% solution of sulfuric acid to make sure that no residual developing solution remains in the traces or through-holes and to minimize the introduction of contaminants into the copper plating tank.
• Attach the cathode clip to the board, making certain that both copper surfaces have good electrical contact to the negative terminal of the plating power supply.
• Turn the power supply on.

Note: The power supply should be adjusted so that, at its lowest setting, it establishes an electrical potential of about 0.25 Vdc when the board is first lowered into the bath. This will help prevent the formation of a low adhesion "electroless" copper layer that might lead to trace peeling and cracking during soldering.

• Lower the board into the plating tank halfway between the two anode banks until the top edge is at least 1" below the surface of the electrolyte.
• Swish the board gently back and forth to drive any trapped air bubbles out of the through holes.
• Turn on the air compressor and adjust the air flow until a uniform blanket of agitation roils the top of the bath on both sides of the board. You only need about 2 CFM (Cubic Feet per Minute) of air flow per square foot of bath surface.
• Slowly ramp up the current (take about 20 sec.) to the value C calculated above.
• Plate the board for 5 minutes to seal the conductive ink with a layer of electrolytic copper.
• Remove the board from the bath and rinse thoroughly to remove any electrolyte.
• Clean the board and laminate both sides with plating resist (photoresist used for etching will also works pretty well).
• Image both sides of the board, being careful that the correct pattern in aligned on each side (component side on the top and solder side on the bottom).

Note: Be sure to leave a bare copper area on both sides of the board so that you can insure good electrical contact with the cathode clip.

• Develop the circuit pattern.
• Reconnect the cathode clip to the board.
• Turn the power supply on.
• Lower the board into the plating tank halfway between the two anode banks until the top edge is at least 1" below the surface of the electrolyte.
• Swish the board gently back and forth to drive any trapped air bubbles out of the through holes.
• Turn on the air compressor and adjust the air flow until a uniform blanket of agitation roils the top of the bath on both sides of the board.
• Slowly ramp up the current (take about 20 sec.) to the value C calculated above.
• Plate the board for ½ the total time (T).
• Turn the current down and flip the board top to bottom and left to right. This will help minimize any plating non-uniformity that results from asymmetric, inconstant plating conditions.
• Reconnect the cathode clip and lower the board back into the bath.
• Plate the board for ½T.
• Remove the board from the bath and thoroughly rinse in the rinse tank to remove most of the electrolyte. Rinse the board under running tap water to remove the rest.

Note: If no outside contamination is introduced, the water in the primary rinse tank can be added back into the plating bath to make up for drag out and evaporative losses. This is crucial to reducing the effluent from this process to near zero.

• Blow dry.
• The plated board is now ready for further processing.

Panel vs. pattern plating

There are two main approaches commonly used when electroplating PCB substrates, panel plating and pattern plating.

During panel plating, the entire copper surfaces on both sides of the substrate, as well as the hole walls are plated up to a desired final thickness. While this requires a fairly hefty current source for even a modest size PCB, the end result is a smooth, bright copper surface that is easy to clean and prepare for later processing. A major problem for folks without access to a photoplotter, is the need to use negative artwork to expose the circuit pattern into the more common contrasting reversing dry-film photoresists (contrast preserving films have been introduced from time to time but never seem to stay around for very long). When you etch a panel plated board, you end up removing most of the material that you plated, so the burden of extra erosion of the anode banks is exacerbated by an increased copper loading in your etchant.

Pattern plating, as the name implies, involves masking off most of the copper surface and plating only the traces and pads of the circuit pattern. Due to the reduced surface area, a much smaller capacity current source is generally needed. Further, when using contrast reversing photopolymer dry-film plating masks (the most common type), a positive image of the circuit is all that is needed. For many prototype PCBs, this artwork can be reliably produced on a relatively inexpensive laser printer or pen plotter. Pattern plating consumes less copper from the anode bank and requires that less copper be removed during etching reducing bath analysis and maintenance. The downside of the technique is that it requires that the circuit pattern be plated with either tin/lead or an electrophoretic resist material prior to etching and then stripped prior to soldermask application. This increases the complexity and adds another set of wet chemical baths to the process.