**SMD LED is a type of surface-mounted semiconductor light-emitting device that offers several advantages, including compact size, wide scattering angle, excellent luminous uniformity, and high reliability. Available in a variety of colors, including white light, SMD LEDs are commonly used in numerous electronic products. One of the primary materials used in the manufacture of SMD LEDs is the PCB board. The development of each new SMD LED product begins with the design of the PCB layout. During the design process, both front and back PCB graphics, the SMD LED assembly drawing, and the finished product drawing must be provided. The designed PCB layout is then handed over to professional LED PCB manufacturers for production. The quality of the design directly impacts the overall product quality and the effectiveness of the manufacturing process. As a result, designing a flawless SMD LED PCB is a challenging task that requires careful consideration of various factors.**

**1. Selection of SMD LED PCB Structure**

SMD LED PCB types are classified based on their structure: through-hole structure, slotted-hole structure, and others. They can also be categorized by the number of chips used in a single SMD LED: single-chip, double-chip, and triple-chip. The main difference between the through-hole structure PCB and the slotted-hole structure PCB is that the former requires cutting in two directions, resulting in a finished electrode with a half-arc shape. In contrast, the slotted-hole structure only requires cutting in one direction. The choice of PCB structure and the number of chips in the SMD LED are typically determined by user requirements. In the absence of specific customer requests, the PCB is usually designed with a slotted-hole structure and a BT substrate.**


**2. Selection of Slotted Hole Direction**

When designing a PCB with slotted holes, it is essential to decide on the direction of the slots. Typically, slotted holes are oriented along the width of the PCB. This design choice helps to minimize deformation of the PCB during the compression molding process.

**3. PCB Outline Size Selection**

Several factors must be considered when selecting the size for each new SMD LED PCB:

1. The number of products required per PCB.

2. Whether the PCB deformation after compression molding remains within an acceptable range.

To optimize production, it is advisable to maximize the number of products per PCB, provided it does not interfere with the manufacturing process. This helps reduce the per-unit cost. Additionally, since the adhesive shrinks during compression molding, leading to PCB deformation, the number of SMD LEDs per group should be kept reasonable. However, the number of groups can be increased to meet the required number of SMD LEDs per board while minimizing deformation. Excessive PCB deformation can make it difficult to cut the board properly, potentially causing adhesive and PCB separation.

The selection of PCB thickness depends on the overall thickness requirements of the SMD LEDs used. The PCB should not be too thick, as it could interfere with wire bonding after die attachment. Conversely, it should not be too thin, as excessive deformation may occur due to the shrinkage of the adhesive during molding.

**4. PCB Circuit Design Requirements**

1. **Die-Bonding Area**: The size of the die-bonding area depends on the size of the wafer. To ensure secure attachment, the die-bonding area should be as small as possible. This increases the adhesion between the adhesive and the PCB, making it less likely for the adhesive to peel off. It is also preferable to position the die-bonding area near the center of the SMD LED circuit board.

2. **Wire Bonding Area**: The wire bonding area should generally be larger than the size of the magnetic nozzle base.

3. **Distance Between Die Bonding and Wire Bonding Areas**: The spacing between the die-bonding and wire-bonding areas should be based on the wire arc. Too large a gap can result in insufficient wire arc tension, while too small a gap may cause the gold wire to contact the chip during wire bonding.

4. **Electrode Width**: The typical electrode width is 0.2mm.

5. **Circuit Wire Diameter**: The diameter of the circuit wire connecting the electrode and die-bonding area should also be considered. Using a smaller wire diameter can enhance the adhesion between the substrate and adhesive.

6. **Via Hole Diameter**: If via holes are used in the PCB design, the minimum via hole diameter is typically 0.2mm (Φ0.2mm).

7. **Slotted Hole Width**: If slotted holes are included in the PCB design, the minimum width of the slot should generally be 1.0mm.

8. **Cutting Line Width**: The cutting process involves a certain thickness of the cutting blade, which can cause some wear on the PCB. It is essential to account for the thickness of the cutting blade in the design of the cutting line width and make adjustments accordingly. Otherwise, the finished product may be narrower than intended after cutting.

**5. Quality Requirements for PCB Substrates**

When designing the PCB, the following technical specifications should be adhered to during production:

1. **Precision**: The board thickness must be consistent, and deviations should be minimized.

2. **Gold-Plated Layer Thickness and Quality**: The gold-plated layer’s thickness and quality must be sufficient to ensure proper bonding during wire bonding, particularly with tensile testing of the gold wire.