Flexible pcb is a highly reliable and excellent flexible printed circuit board made of polyimide or polyester film. It has the characteristics of high wiring density, lightweight, thin thickness, and good bendability. Due to its particularity, various aspects need to be paid attention to when flexible pcb design.
Table of Contents:
1. Overlap of pads
2.the abuse of the graphics layer
3. the random placement of characters
4. the setting of the single-sided pad aperture
5. drawing pads with filler blocks
6.3the electrical ground layer arrows rc jet is also a flower pad and a connection
7.the processing level is not clearly defined
8. There are too many filler blocks in the design or the filler blocks are filled with very thin lines
9. the surface mount device pad is too short
10. The spacing of large-area grids is too small
11. The distance between the large area of copper foil and the outer frame is too close
12. The design of the outline frame is not clear
13. Uneven graphic design
14. When the copper area is too large, grid lines should be used to avoid blistering during SMT.
1. Overlap of pads
a. In the flexible pcb design, 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.
b. Two holes in the multilayer board overlap. For example, one hole is an isolation disk and the other hole is a connection pad (flower pad) so that the film will appear as an isolation disk after drawing the film, resulting in scrap.
2.the abuse of the graphics layer
a. Some useless connections were made on some graphics layers. The original four-layer board was designed soldering gun with more than five layers of wiring, which caused misunderstandings.
b. The flexible pcb design saves time and trouble. 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 line. In this way, when the light drawing data is performed, because the Board layer is not selected, Missing the connection and breaking the circuit, or short-circuiting due to the selection of the marking line of the Board layer, so the integrity and clarity of the graphics layer should be kept in the design.
c. Violation of conventional design, such as the component surface design in the bottom layer and welding surface design in Top, causing inconvenience.
3.the random placement of characters
a. 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.
b. In the design process of flexible pcb, the character design is too small, which makes screen printing difficult, and too large will make the characters overlap each other and make it difficult to distinguish.
4.the setting of the single-sided pad aperture
a. 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.
b. Single-sided pads should be specially marked for drilling holes.
5.drawing pads with filler blocks
In the design of flexible pcb, the pads drawn with filler blocks can pass the DRC inspection when designing the circuit, but it is not good for processing. Therefore, the solder mask FMS RC jet data cannot be directly generated by similar pads. When the solder resists is applied, the filler block area will be It is covered by the solder resist, which makes it difficult to solder the device.
6. the electrical ground layer is also a flower pad and a connection
Because the power supply is designed as a flower pad, the ground layer is opposite to the image on the actually printed board, and 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 to short-circuit the two sets of power supplies and to block the connection area (to separate a set of power supplies).
7.the processing level is not clearly defined
a. The single-sided design of flexible pcb is 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.
b. 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 filler blocks in the design or the filler blocks are filled with very thin lines
a. The Gerber data is lost, and the Gerber data is incomplete.
b. 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. The test pins must be installed in a staggered position, such as pads. The design is too short, although it does not affect the device installation, it will make the test pin staggered.
10. The spacing of large-area grids is too small
Inflexible pcb design, the edges between the same lines that make up a large area of grid lines 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 disconnection.
11. The distance between the large area of copper foil and the outer frame is too close
When designing flexible pcb, the distance between the large area copper foil and the outer frame should be at least 0.2mm or more, because when milling the shape of the copper foil, it is easy to cause the copper foil to warp and the solder resists falling off caused by it.
12. The design of the outline frame is not clear
Some customers have designed contour lines for the Keep layer, Board layer, Top over layer, etc., and these contour lines do not overlap, which makes it difficult for pcb manufacturers to determine which contour line shall prevail.
13. Uneven graphic design
When pattern plating is performed, the plating layer is uneven, which affects the quality.
14. When the copper area is too large, grid lines should be used to avoid blistering during SMT.
The above is to introduce the matters needing attention in the design of flexible pcb.
