PCB News - Special term for PCB circuit design of smt factory

Special term for PCB circuit design of smt factory
We are a professional smt factory established in Shenzhen in 2004. There are many special terms about PCB circuit design. The following editors will share with you one by one.
1. Blind Via Hole

Refers to the complex multi-layer board in the smt factory, some of the via holes are deliberately incompletely drilled because they only need a certain layer of interconnection. If one of the holes is connected to the ring of the outer board, this A special hole such as a cup-shaped blind alley is called a "Blind Hole" (Blind Hole).

2. Artwork film

In the circuit board industry, this word often refers to black and white negatives. As for the brown "Diazo Film" (Diazo Film), it is also named after Phototool. The negatives used in PCB can be divided into "original negatives" MasterArtwork and re-photographed "working negatives" WorkingArtwork, etc.

3. Basic Grid

Refers to the vertical and horizontal grid where the conductor layout of the smt factory is located during the circuit board design. In the early days, the grid spacing was 100 mil. At present, due to the prevalence of fine lines and dense lines, the basic grid spacing has been reduced to 50 mils.

4. Annular Ring

Refers to the copper ring that is flatly attached to the board surface around the wall of the through hole. The hole ring on the inner plate is often connected to the outer ground by a cross bridge, and is more often regarded as the end of the line or the station. On the outer layer board, it can be used as a soldering pad for component pin soldering, in addition to being used as a circuit crossing station. There are Pad (with circle), Land (independent point) and so on that are synonymous with this word.

5. Block Diagram circuit system block diagram

It means that the smt factory will assemble the board and the various components required by the square or rectangular empty frame on the design drawing, and use various electrical symbols to contact the relationship between the frames one by one, so that the composition has System architecture diagram.

6. Bomb Sight bullet mark

Originally refers to the aiming screen where bombers dropped bombs. During the production of the negatives of the PCB, for the purpose of alignment, the upper and lower two-layer alignment targets are also set up at each corner. The more accurate official name should be called Photographers' Target.

7. Break-away panel can be disconnected

Refers to many small circuit boards in the smt factory. For the convenience of plug-in, component placement, soldering and other operations on the downstream assembly line, in the PCB manufacturing process, they are specially combined on a large board for various processing . When the work is completed, the method of jumping blades is used to perform a local cutting shape (Routing) disconnection between the independent small plates, but several "Tie Bar or Break-away Tabs" with sufficient strength are retained, and they are connected. Drill a few more small holes between the sheet and the edge of the board; or cut V-shaped notches up and down to facilitate the separation of the boards after the assembly process is completed. This kind of small board joint assembly method will be more and more in the future, IC card is an example.

8. Buried Via Hole

Refers to the local vias of the multi-layer board of smt factory. When they are buried in the inner layer of the multi-layer board, they become "internal vias" and are not "connected" with the outer board, which are called buried vias or buried vias for short.

9. Bus Bar

Refers to the cathode or anode rod itself on the electroplating tank of the smt factory, or the cable to which it is connected. In the circuit board "in process", the outer edge of the gold finger is close to the edge of the board, the original connecting wire (which must be covered during the gold plating operation), and a small narrow piece (all for saving gold (It is necessary to reduce the area as much as possible) to connect with each finger. This kind of conductive connection is also called Bus Bar. The small piece where each individual finger is connected to the Bus Bar is called Shooting Bar. When the board is finished cutting the shape, both will be cut off together.

10. CAD computer-aided design

Computer AidedDesign uses special software and hardware to digitally lay out the circuit board, and uses an optical plotter to convert the digital data into original film. This kind of CAD is far more accurate and convenient for the pre-manufacturing engineering of the circuit board than the manual method.

11. Center-to-Center Spacing

Refers to the Nominal Distance (Nominal Distance) from the center to the center of any two conductors on the board. If the conductors arranged in a row have the same width and spacing (such as the arrangement of gold fingers), then this "center-to-center spacing" is also called pitch.

12. Clearance room, clearance, empty ring

Refers to the inner layer of the multilayer board, if the conductor surface is not connected with the hole wall of the through hole, the copper foil around the through hole can be etched away to form an empty ring, especially called "empty ring". In addition, the distance between the green paint printed on the outer board and each ring is also called Clearance. However, due to the gradual increase in the density of the current board surface, the original room for this green paint has also been forced to be almost empty.

13. Component Hole

Refers to the through-holes for inserting parts on the board. The hole diameter of this pin hole is about 40 mils on average. Now that SMT has become popular, the number of large-aperture jacks has been gradually reduced, and only a few gold pin holes of the connectors need to be plug-welded, and most of the remaining SMD parts have been surface-mounted.

14. Component Side

In the early days when the circuit board was fully inserted with through-holes, the parts must be installed on the front of the board, so the front was also called the "component surface". The reverse side of the board is also called "Soldering Side" because only the tin wave of wave soldering passes through. At present, SMT boards have to attach parts on both sides, so there is no such thing as "component side" or "solder side", it can only be called front side or back side. Usually the name of the manufacturer of the electronic machine is printed on the front, and the UL code and production date of the circuit board manufacturer can be added on the back of the board.

15. Conductor Spacing conductor spacing

Refers to the span of a certain conductor on the circuit board surface from its edge to the edge of another nearest conductor, which is called the conductor spacing, or colloquially called the spacing. In addition, Conductor is a general term for various forms of metal conductors on circuit boards.

16. Contact Area contact resistance

On the circuit board, it refers specifically to the contact point between the golden finger and the connector, which is the resistance that appears when the current passes. In order to reduce the formation of oxides on the metal surface, usually the male gold finger part and the female clip of the connector need to be plated with metal to prevent the occurrence of "load resistance". The plugs of other electrical products are squeezed into the socket, or there is contact resistance between the guide pin and its socket.

17. Corner Mark

On the negative of the circuit board, special marks are often left at the four corners as the actual boundary of the board. If the inner edge of these marks is connected, it is the boundary line of the contour of the finished board.

18. Counterboring fixed depth reaming, counterboring

The circuit board can be locked and fixed in the machine with screws. For this matching non-through hole (NPTH), the hole must be a "reamed hole" that can accommodate the nut, so that the entire screw can sink into the board surface. In order to reduce the obstacles caused by appearance.

19. Crosshatching cross area

For some large-area conductor areas on the circuit board surface, in order to get better adhesion to the board surface and the green paint, the copper surface of the sensing part is often turned away, leaving many cross lines that cross vertically and horizontally. Like the structure of a tennis racket, this will resolve the risk of floating away from a large area of copper foil due to thermal expansion. The etched cross pattern is called Crosshatch, and this improved method is called Crosshatching.

20. Countersinking cone reaming, horn hole

It is another type of screw hole for locking. It is mostly used in woodworking furniture, but rarely in the precision electronics industry.

21, Crosssection Area

The cross-sectional area of the circuit on the circuit board will directly affect its current-carrying capacity, so it should be included in the design first. The copper surface of the sensing part is often turned away, leaving many cross lines that cross vertically and horizontally, such as a tennis ball. The structure of the shot is the same, so that the large area of copper foil can be resolved by the floating crisis due to thermal expansion. The etched cross pattern is called Crosshatch, and this improved method is called Crosshatching.

22, Current-Carrying Capability

Refers to the wires on the board that can continuously pass the maximum current intensity (amperes) under specified conditions without causing degradation of the electrical and mechanical properties of the circuit board (Degradation). The amperage of the maximum current is The "current carrying capacity" of the line.

23, Datum Reference benchmark reference

In the process of PCB manufacturing and inspection, in order to be able to correctly position the negative pattern on the board surface, a certain point, line, or hole surface is specially selected as the reference reference for its graphics, called Datum Point, Datum Line, Also known as Datum Level (Plane), also known as Datum Hole.

24, Dummy Land dummy soldering pad

In order to adjust the height of the existing parts during assembly, the board surface under the belly of some parts needs to be raised so that the glue can have better adhesion. Generally, the etching technology of the circuit board can be used to deliberately leave the board there. The "fake copper pad" that is not connected to the power supply and only used as a booster is called Dummy Land. However, sometimes due to poor design on the board surface, a large area of the substrate surface without a copper layer will appear, with a few through holes or lines distributed. In order to avoid the excessive current concentration of these independent conductors during copper plating and various defects, some non-functional dummy pads or false wires can also be added to distribute some current during electroplating, so that the current density of a little independent conductor Not too high, these copper surfaces are also called Dummy Conductors.

25. Edge Spacing

Refers to the vacant ground from the edge of the board to the "nearest conductor line". The purpose of this section of vacant ground is to avoid the problem of short-circuiting with other parts of the machine due to the conductor being too close to the board edge. The safety certification of the United States UL, Special attention is paid to this project. Defects such as delamination of white edges of general boards cannot penetrate into half of the width of this "edge".

26, Edge-Board contact plate edge gold finger

It is the outlet for the entire board to communicate with the outside. Usually, there are two symmetrical sides of the board edge, which can be plugged into the matching board edge connector.

27. Fan Out Wiring／Fan in Wiring

Refers to the conductors such as lines and through holes drawn from the solder pads around the QFP, so that the soldered parts can complete the interconnection work with the circuit board. Because the rectangular pads are arranged very tightly, the external connection must use the open space inside or outside the rectangular pad square ring to route in a fan-shaped manner, which is called "fan-out" or "fan-in". Lighter, thinner, shorter and denser PCBs can be provided with more solder pads on the outer layer to accept more parts, and the wiring required for interconnection can be hidden on the next layer. The bonding pads and leads between different levels are directly connected with the blind holes in the pads, and there is no need to do fan-out and fan-in wiring. At present, many mobile phone boards of high-function small wireless phones adopt this new type of laminate. And wiring method.

28. Fiducial Mark optical target, reference signal

In order to assemble downstream on the board and facilitate the operation of its visual aid system, a triangular "optical target" is added to the upper right and lower left of each large IC on the open space on the outer edge of each solder pad at the board assembly position to assist An example is the placement machine for optical positioning. In the PCB manufacturing process, more than two reference marks are often added for the orientation alignment of the film and the board surface.

29, Fillet inner fillet

Refers to two planes or two straight lines, in terms of arcs filled at their perpendicular intersections. In the circuit board, it often refers to the solder joints of the parts of the pins, or the inner circle filling of the intersections of the T-shaped or L-shaped lines on the board surface, so as to enhance the mechanical strength and the convenience of current flow.

30, Film negatives

Refers to the film that has circuit graphics. There are usually two thicknesses of 7mil and 4mil. The photosensitive film includes black and white silver halide, and brown or other colored azo compounds. This term is also called artwork.

31, Fine Line

According to the current technical level, the four lines between holes or those with an average line width of 5-6 mils or less are called thin lines.

32. Fine pitch, dense line distance, dense pad distance

Where the lead pitch is equal to or less than 0.635mm (25mil), it is called close pitch.

33. Finger fingers (continuous arrangement of contacts on the edge of the board)

In order to enable the functions of the whole assembly board to be connected to the outside on the circuit board, the "male" gold-plated continuous contact on the edge of the board can be inserted and clamped on the "female" continuous receiver of another system to enable To achieve the purpose of interconnection between systems. The official name of Finger is "Edge-Board Contact".