PCB assembly process is based on the production data of the PCB design and PCB manufacturing specifications, good PCB design is conducive to the subsequent PCB assembly processing, while incomplete PCB design will affect the processing, and even affect the quality of PCB assembly products.
1、Soldering can not have silkscreen, SMT pads on the silkscreen will affect the quality of the assembly.
However, sometimes the silkscreen marking of some critical ICs is necessary because it can be used to identify the deviation of the soldering quality (especially for some highly valuable QFN components), so that the edge components of the IC can be placed in the corner of the SMT area to avoid any overlapping problem of the soldering pads.
Change the IC edge markings to avoid any overlapping of solder pads.
SMT Screen Print Error Design
2、Component/PCB board edge/copper foil spacing: the minimum distance between copper foil and board edge is 0.5mm, the minimum distance between component and board edge is 5.0mm, and the minimum distance between pad and board edge is 4.0mm.
3、Mark points and the need for holes: Mark points (red arrows in the figure below) need to be placed on a single PCB or panel, used as a reference position for solder paste printing or placement machines in the assembly machine, to ensure that the PCB assembly process can be accurately soldered electronic components.
Typically the minimum diameter of a circular Mark is 0.1mm.
PCBA holes are also non-plated holes, normally 3.0mm in size, with a minimum of 3 holes, which are placed on the PCB board. Used to fix the PCB board, so that it is in the electronic testing and other production processes PCB can not be free to move, which is to facilitate the PCB production and manufacturing process necessary for the hole.
4、when designing double-sided boards, pay attention to the components with metal shells. when the shells are in contact with the PCB during DIP, the top pads cannot be opened, and must be coated with soldermask or silkscreen oil.
5、Do not place jumpers under ICs, motors, potentiometers or other components with large metal cases.
6、Electrolytic capacitors can not contact with heat-generating components, such as high-power resistors, thermistors, transformers, heat sinks and so on. The minimum distance between electrolytic capacitors and heat sinks is 10mm, and the interval between other components and heat sinks is 2.0mm.
7、large components (such as transformers with a diameter of 15mm or more, electrolytic capacitors, high-current sockets) should increase the pad.
8、The minimum alignment width / spacing: 0.1mm, if the line width / spacing is less than 0.1 / 0.1mm, the manufacturing cost will increase accordingly. Of course, if the product is a high integrated circuit design, and the physical size of the PCB board is limited, it is necessary to consider a smaller alignment width / spacing, and manufacturing costs in a reasonable range of areas.
9、Screw holes within a radius of 5mm should not be copper foil (except for grounding) and components (or according to the structure of the requirements of the diagram).
10、The general through-hole mounting components of the pad size (diameter) is twice the hole diameter. Minimum 1.5mm for double-sided panels and 2.0mm for single-sided panels. if there is no round pad, you can use a waist pad.
11、If the pad centre distance is less than 2.5mm, the surrounding pads should be wrapped in silkscreen oil, silkscreen oil width of 0.2mm.
12、For components that need to be soldered through the tin furnace, the pads should be away from the tin position. The direction of the pads and the direction of the tin over the opposite direction, for 0.5mm to 1.0mm. mainly used for back-soldering pads on one side, to avoid clogging over the furnace.
13、Large area PCB design (greater than about 500cm or more), in order to prevent the PCB board over the tin furnace when bending, in the middle of the PCB board without components should be left 5mm to 10mm gap (can walk the line) for the addition of bending rib, to prevent over the tin furnace when bending.
14、In order to reduce the solder joints short-circuit, all double-sided holes are not open solder resist window.
15、SMD components or through-hole soldering components to maintain sufficient physical spacing between the otherwise avoid any potential edge overlap problems, which will bring additional trouble to the SMD assembly process (deviation soldering problems).
