Design of SMD LED PCB
SMD LED is a new type of surface mount semiconductor light-emitting device, with a small size, scattering angle, luminous uniformity is good, high reliability, light color, including white, including a variety of colors, it is widely used in All kinds of electronic products. LED PCB board is one of the main materials for manufacturing SMD LED. Each new chip-type LED product development is from the design of LED PCB board drawings began in the design should be given the PCB front and back graphics and patch-type LED PCB assembly drawings and finished product plans, and then design a good LED PCB board drawings To the professional production of LED PCB board manufacturers system board, the design of a direct impact on the quality of the product and the implementation of manufacturing processes. Therefore, the design of a flawless patch-type LED PCB board is not an easy thing, must take into account the many factors that affect the design. To this end, from the following aspects of the SMD LED PCB board design to explore.
First, the patch-type LED PCB board structure selection
Chip type LED PCB board type according to the structure: a through-hole structure, digging slot structure; according to a single chip-type LED used in the number of chips: single crystal, double crystal and three crystal type. Through the hole structure PCB board and digging hole structure PCB board difference is: the former need to cut two cutting direction, a single finished electrode for the semi-arc type; the latter cut only one direction of cutting. Choose what kind of structure of the PCB board and SMD LED chip with a few ways is based on the requirements of market users. When the user does not make a special request, the general choice of digging hole structure design PCB board. PCB substrate for the BT board.
Second, the choice of the direction of digging slot
, you must consider which direction to select the slot. In general, the grooved hole is designed along the width of the LED PCB board, because it can make the die after molding the PCB board to produce the smallest deformation.
Third, the LED PCB board size selection
The choice of the size of each new SMD LED PCB board must be considered: ① the number of products designed on each PCB board. ② whether the deformation of the PCB board after molding is within the acceptable range.
Without affecting the production process, the number of products on each PCB board as much as possible design, which will help reduce the cost of a single product. And because the compression molding after the plastic will shrink, PCB board prone to deformation, so the PCB board in the design should also consider the number of each patch LED can not be too much, but the number of groups can be designed more points. This can meet the single PCB board on the number of SMD LED requirements, and will not make the compression molding after the colloid shrinkage caused by the PCB board deformation is too large. PCB board deformation caused by the PCB board can not be cut and cut after the colloid and PCB board easy to peel.
PCB board thickness selection is based on the user to use the overall thickness of the SMD LED requirements to determine. PCB board thickness can not be too thick, too thick will cause solid crystal can not wire; PCB thickness can not be too thin, too thin will cause compression molding after colloid shrinkage, PCB board deformation is too large.
To 0603 specifications for the thickness of 0.6mm ordinary SMD LED products as an example to illustrate. If the thickness of 0.3mm PCB board, the colloid part of the thickness of only 0.3mm, and then select the thickness of 0.28mm wafer for solid crystal, the overall thickness of 0.58mm, it can not be wire operation. If the choice of thickness of 0.1mm PCB board, colloidal part of the thickness of 0.5mm, after the compression molding due to colloid thick, colloidal shrinkage significantly, and PCB board is thin, this will make the PCB board deformation is too large. Therefore, in the design of PCB thickness must choose a suitable thickness, both can make the same PCB board for different thickness chip chip LED.
Fourth, LED PCB board design requirements
1, solid crystal area: solid crystal area size design is determined by the size of the chip. In order to meet the security can be a good solid chip, the solid crystal area to be as small as possible design. So that after the stamper colloid and PCB board will be better adhesion, easy to produce colloidal and PCB board peeling phenomenon, but also consider the solid crystal area as much as possible in the design of a single patch LED circuit board in the middle position.
2, the wire area: the wire area is basically greater than the bottom of the magnetic size.
3, solid crystal area and the distance between the wire area: solid crystal area and the distance between the wire to determine the line to the arc, the distance caused by the General Assembly line arc tension is not enough, the distance will cause the wire when the gold wire contact with the chip.
4, electrode width: electrode width is generally 0.2mm.
5, the circuit diameter: connecting the electrode and solid crystal area of the circuit diameter should also consider the size of the problem. The use of small diameter can increase the adhesion of the substrate and colloid.
6, through the hole diameter: If the use of through-hole design PCB board, through-hole aperture minimum is generally Φ0.2mm.
7, digging hole diameter: If the use of through-hole design PCB board, digging slot width minimum is generally 1.0mm.
8, cutting line width: cutting because the cutting blade has a certain thickness of the existence of PCB board will be part of the wear after cutting, so the width of the cutting line to take into account the thickness of the cutting blade in the PCB board design to compensate, Otherwise the width of the finished product after cutting is too narrow.
In addition, the pore size of the positioning hole and the like are also considered. Generally a PCB board can be designed within the circuit number of the number of products designed for the double number.
Fifth, the PCB substrate quality requirements
PCB board design, LED PCB board should be made the following technical description:
1, requires sufficient accuracy: the requirements of thickness unevenness <± 0.03mm, positioning hole on the circuit board deviation <± 0.05mm.
2, the thickness and quality of gold-plated layer must ensure that the gold wire after the tensile test> 8g.
3, LED PCB board made of finished products, the requirements of the surface without sticky, after the mold and colloid adhesion between the good.