Microwave Tech - Common problems in circuit design of soft and hard board

1. Overlap of pads
1. The overlap of the pads (except the surface mount pads) means the overlap of the holes. During the drilling process, the drill bit will be broken due to multiple drilling in one place, resulting in damage to the holes.
2. The two holes in the rigid-flex board overlap. For example, one hole is the isolation disk and the other is the connection disk (flower pad). After drawing the film, it will appear as an isolation disk, resulting in scrap.
2. The abuse of the graphics layer
1. Some useless connections were made on some graphics layers. It was originally a four-layer board but designed with more than five layers of wiring, which caused misunderstandings.
2. Save trouble during design. Take the Protel software as an example to draw the lines on each layer with the Board layer, and use the Board layer to mark the lines. In this way, when performing light drawing data, because the Board layer is not selected, it is omitted. The connection is broken, or it may be short-circuited due to the selection of the marking line of the Board layer, so the integrity and clarity of the graphics layer is maintained during design.
3. Violation of conventional design, such as component surface design on Bottom layer and soldering surface design on Top, causing inconvenience.
3. Random placement of characters
1. The SMD soldering pad of the character cover pad brings inconvenience to the continuity test of the printed board and the soldering of the components.
2. If the character design is too small, it will be difficult for screen printing. If it is too large, the characters will overlap each other and be difficult to distinguish.

4, single-sided pad aperture setting
1. Single-sided pads are generally not drilled. If the drilling needs to be marked, the hole diameter should be designed to be zero. If the numerical value is designed, then when the drilling data is generated, the coordinates of the hole appear at this position, and there is a problem.
2. Single-sided pads such as drilling should be specially marked.

5. Draw pads with filler blocks

Drawing pads with filler blocks can pass the DRC inspection when designing the circuit, but it is not possible for the processing of soft and hard boards. Therefore, the solder mask data cannot be directly generated by the similar pads. When the solder resist is applied, the area of the filler block will be blocked. Flux coverage makes it difficult to solder the device.

6. The electrical ground is also a flower pad and a connection
Because the power supply is designed as a pattern pad, the ground layer is opposite to the image on the actual printed board. All the connections are isolated lines. The designer should be very clear about this. By the way, you should be careful when drawing isolation lines for several sets of power supplies or grounds, not to leave gaps, short-circuit the two sets of power supplies, and block the connection area (to separate a set of power supplies).

7, the processing level is not clearly defined
1. The single-sided board is designed on the TOP layer. If the front and back are not specified, the manufactured board may not be easy to be soldered with components installed.
2. For example, a four-layer board is designed with four layers of TOP mid1 and mid2 bottom, but it is not placed in this order during processing, which requires explanation.

8. There are too many filling blocks in the design or the filling blocks are filled with very thin lines
1. The gerber data is lost, and the gerber data is incomplete.
2. Because the filling blocks are drawn one by one with lines when processing the light drawing data, the amount of light drawing data generated is quite large, which increases the difficulty of data processing.

9, the surface mount device pad is too short
This is for continuity testing. For surface mount devices that are too dense, the spacing between the two pins is quite small, and the pads are also quite thin. To install the test pins, they must be staggered up and down (left and right), such as pads. The design is too short, although it does not affect the device installation, but it will make the test pin staggered.
10. The spacing of large-area grids is too small

The edges between the same lines that make up a large-area grid are too small (less than 0.3mm). During the manufacturing process of the printed board, the image transfer process will easily produce a lot of broken films attached to the board after the image is developed, causing the line to break.
11, the distance between the large area copper foil and the outer frame is too close

The distance between the large area copper foil and the outer frame should be at least 0.2mm, because when milling the shape, if it is milled to the copper foil, it is easy to cause the copper foil to warp and the solder resist falling off caused by it.
12. The design of the outline frame is not clear

Some customers have designed contour lines for Keep layer, Board layer, Top over layer, etc., and these contour lines do not overlap, which makes it difficult for the rigid-flex board manufacturers to judge which contour line shall prevail.

XIII. Uneven graphic design

In the process of pattern plating, the plating layer is not uniform, which affects the quality.
14 Use grid lines when the copper area is too large to avoid blistering during SMT.