**1. Positioning Holes in PCB Manufacturing and Assembly**

In both the PCB design and the semi-automatic insertion and ICT testing processes during assembly, it is essential for the PCB to include two to three positioning holes at the corners.

**2. Effective Use of PCB Splicing to Enhance Production Efficiency and Flexibility**

Assembling PCBs with small dimensions or irregular shapes presents various challenges. To address this, the common practice is to splice several smaller PCBs together to create a larger, more manageable PCB.

PCBs with a single-sided dimension smaller than 150mm are typically joined together in configurations such as two-piece, three-piece, or four-piece assemblies. This approach allows the overall PCB to fall within the ideal processing range, typically 150mm–250mm in width and 250mm–350mm in length, which is more suitable for automated assembly.

Another splicing technique involves joining PCBs with surface-mounted devices (SMD) on both sides into a larger panel. This method, known as “Yin-Yang splicing,” is often used to reduce costs associated with the use of separate PCB panels. Instead of requiring two screens, only one is needed for this spliced assembly.

Additionally, when programming the placement machine, the efficiency of PCB programming is improved when using the Yin-Yang splicing method.

To connect the sub-boards, options such as double-sided engraved V-slots, long slots, and round holes can be used. However, the design should ensure that the separation lines are as straight as possible to facilitate the final splitting process. Care should also be taken to avoid placing the separation edge too close to PCB traces, as this could risk damaging the PCB during the splitting process.

An alternative and cost-effective form of splicing is related to the stencil mesh pattern, rather than the PCB itself. With the advent of fully automated solder paste printers, advanced printers now support multi-sided PCB mesh patterns on a 790mm x 790mm stencil, allowing for the printing of multiple products on a single stencil. This method is particularly cost-effective, especially for manufacturers dealing with small batches and a variety of product types.

**3. Design Considerations for Testability**

Testability design in SMT is primarily concerned with accommodating the current ICT equipment limitations. During the design of both the circuit and surface-mounted PCB (SMB), potential testing challenges in later stages of product manufacturing must be considered. To enhance testability, it is crucial to address both process design and electrical design aspects.

**4. Process Design Requirements**


1. Positioning accuracy, substrate manufacturing processes, substrate size, and probe type are all factors that influence detection reliability.

2. **Precise Positioning Holes**: It is important to set accurate positioning holes on the substrate, with an error tolerance within ±0.05mm. At least two positioning holes should be included, and the distance between them should be optimized. Use non-metallized positioning holes to prevent solder plating thickening that could lead to tolerance issues. If the substrate is produced as a single unit and then tested separately, positioning holes must be provided on both the main board and each individual substrate.

3. The diameter of the test points should be no less than 0.4mm, and the distance between adjacent test points should ideally be above 2.54mm, with a minimum of 1.27mm.

4. Do not place components with a height greater than *mm on the test surface. Overly tall components can interfere with proper contact between the test fixture probe and the test point.

5. It is best to position test points at least 1.0mm away from any component to avoid damaging the probe or the component itself. There should be no components or test points within 3.2mm around the perimeter of the positioning hole.

6. Test points should not be placed within 5mm of the edge of the PCB. This 5mm margin is necessary to ensure proper fixture clamping. This is typically required on the same process side for conveyor belt and SMT production equipment.

7. All test points should ideally be tinned or use soft, easily penetrable, and non-oxidizing metal conductors to ensure reliable contact and extend the probe’s service life.

8. Test points must not be covered by solder resist or ink markings, as this would reduce the contact area and decrease the reliability of the test.

**Electrical Design Requirements**

9. It is recommended to route the SMC/SMD test points from the component surface to the soldering side via vias, with via hole diameters greater than 1mm. This approach allows for testing using a single-sided needle bed, thus reducing the cost of online testing.

10. Each electrical node must have a corresponding test point, and each IC should have dedicated POWER and GROUND test points placed as close to the IC as possible, ideally within 2.54mm.

11. When placing test points on circuit traces, the trace width can be increased to 40 mils to accommodate the probe.

12. Test points should be evenly distributed across the PCB. If probes are concentrated in one area, excessive pressure may deform either the board or the needle bed, potentially preventing some probes from making proper contact with their test points.

13. The power supply circuit should include test break points at different locations. This allows for quicker and more accurate detection of faults, such as when a decoupling capacitor or other components short to the power supply. When designing the breakpoints, ensure that power carrying capacity is restored after testing.

14. Extension wires or via pads should be used to set test pads near component leads or test nodes. Test points should never be placed on component solder joints, as this could cause false solder joints to be pressed under the probe’s pressure, masking the defect. This is referred to as the “fault masking effect.”

15. Due to probe sway caused by positioning errors, the probe may make direct contact with the endpoint or pin of a component, potentially damaging it.

16. The above guidelines focus on the manufacturability of PCB layout and design, and are intended to help improve the quality and reliability of testing processes.

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