PCB design FAQ
First, the overlap of the pads
1. Overlap of pads (except surface mount pads) means overlap of holes. During the drilling process, the drill bit breaks due to a plurality of holes in one hole, resulting in damage to the hole.
2. The two holes in the multilayer board overlap, for example, one hole is a separator and the other hole is a connection plate (flower pad), so the negative film is formed as a spacer disk, resulting in scrap.
Second, abuse the graphics layer
1. Some useless connections have been made on some graphics layers. Initially, the design of the four-layer board exceeded five layers, which caused misunderstanding.
2, design saves time and trouble, take Protel software as an example, each layer of the layer is drawn with a layer, and the layer is used to draw lines, so when selecting light drawing data, because the board does not select a layer, it Was omitted. The design layer is kept intact and clear by selecting the marking lines of the Board layer for wire and disconnect or short circuit.
3. Violation of conventional design, such as the surface design of the underlying components, the welding surface is designed at the top, causing inconvenience.
Third, randomly placed characters
1. Character cover SMD soldering parts are inconvenient for switching test and component soldering of printed circuit boards.
2, the character design is too small, which makes the screen printing difficult, too much to make the characters overlap each other, it is difficult to distinguish.
Four, single-sided pad aperture setting
1. Single-sided mats are usually not drilled. If you want to mark a hole, you should design the hole to zero. If a numerical value is designed, the coordinates of the hole appear at this position when the drilling data is generated, and a problem occurs.
2. Single hole pads, such as drill holes, should be specially marked.
Fifth, pad with padding
When designing the production line, use a mat to draw a mat to pass the DRC inspection, but it is not suitable for processing. Therefore, the pad cannot directly generate solder resist data. When a solder resist is applied, the pad area will be covered by the solder resist, making the device difficult to solder.
Sixth, the electrical ground plane is a flower mat and is connected
Since the power supply is designed as a flower mat, the ground plane is opposite to the image on the actual printed circuit board, and all connections are isolated lines, which the designer should be very clear about. By the way, when drawing several sets of power supplies or multiple grounded isolation lines, care should be taken not to leave gaps to avoid shorting the two groups of power supplies and the connection area cannot be blocked (to separate a set of power supplies).
Seven, the definition of processing level is not clear
1. Single panel design in the TOP layer. If you do not explain the positive and negative, the board may not be soldered.
2. For example, a four-layer board design uses four layers of TOP mid1 and mid2 bottoms, but processing is not performed in this order, which requires explanation.
Eight, too many filled blocks in the design or filled with very thin line filling blocks
1. The phenomenon of loss of light drawing data is lost, and the light drawing data is incomplete.
2. Since the filling block is drawn line by line during the light drawing data processing, the amount of light drawing data generated is very large, which increases the difficulty of data processing.
Nine, surface mount device pads are too short
This is for switch testing. For surface mount devices that are too dense, the spacing between the two legs is very small and the pads are very thin. Test pins must be mounted up and down (left and right), such as pads. The design is too short, although it does not affect the installation of the device, but it will make the test pin wrong.
Ten, the spacing of large area grids is too small
The edge between the large area grid line and the same line is too small (less than 0.3 mm). During the manufacturing process of a printed circuit board, the image transfer process may cause a large amount of broken film to adhere to the circuit board after the completion of the shadow, resulting in disconnection.
Eleven. The distance between the large area copper foil and the outer frame is too close.
The large-area copper foil should be at least 0.2 mm or more from the outer frame, because when the shape is milled onto the copper foil, it is easy to cause the copper foil to rise and the resulting solder resist to fall off.
Twelve, the shape of the border design is not clear
Some customers have designed contours to maintain layers, slabs, top layers, and so on. These contours do not overlap, which makes it difficult for PCB manufacturers to determine which contour is limited.
Thirteen, uneven graphic design
In the case of pattern plating, the plating is uneven and affects the quality.
Fourteen, the shape of the hole is too short
The length/width of the shaped hole should be ≥2:1 and the width should be >1.0mm. Otherwise, the drill machine easily breaks the drill bit when machining the shaped hole, which makes processing difficult and increases cost.