Automatic Detection Technology of Printed Circuit Board: Needle Bed Test Method

With the rise of surface mount technology, the packaging density of circuit boards has significantly increased. As a result, the automatic detection of circuit boards has become essential and cost-effective, even for low-density boards. When it comes to complex circuit board inspections, two common methods are the needle bed test method and the double probe or flying probe test method. Today, we will focus on the needle bed test method.

Needle Bed Test Method:

In the needle bed test method, a probe with a spring is attached to each detection point on the circuit board. The spring ensures that each probe applies a pressure of 100-200g to establish proper contact with the detection points. These probes are grouped together to form “needle beds.” Through the control of detection software, the detection points and signals can be programmed. In practice, only the probes corresponding to the test points are installed. While it is feasible to test both sides of the circuit board simultaneously using this method, all inspection points should be located on the soldering surface of the board during the design phase. The needle bed tester is expensive and challenging to maintain. Depending on the specific requirements, probes are chosen for different needle arrangements.

A basic general-purpose grid processor comprises a drilled board with pins positioned at 100, 75, or 50 mils. These pins serve as probes and establish direct mechanical connections with electrical connectors or nodes on the circuit board. If the pads on the circuit board align with the test grid, a polyester film with perforations based on specifications is inserted between the grid and the board to facilitate the design of specific probes. Continuity detection is accomplished by accessing the endpoints of the grid, identified as the x-y coordinates of the pad. Each network on the circuit board undergoes continuity testing, completing an individual test. However, the effectiveness of the needle bed test method is limited by the proximity of the probes.

Latest Developments:

• Advancements in needle bed test technology have led to the development of more precise and efficient probes.
• New software algorithms are being implemented to enhance the programming and control of detection points in the needle bed test method.
• Researchers are exploring ways to overcome the limitations posed by probe proximity in order to improve the overall effectiveness of the needle bed test method.