Automatic Detection Technology of Printed Circuit Board: Needle Bed Test Method
With the introduction of surface mount technology, the packaging density of circuit boards has increased rapidly. Therefore, even for low-density, ordinary circuit boards, the automatic detection of circuit boards is not only fundamental but also cost-effective. In 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 discuss the needle bed test method.
Needle Bed Test Method:
In this method, a probe with a spring is connected to each detection point on the circuit board. The spring ensures that each probe exerts a pressure of 100-200g to ensure proper contact with each detection point. These probes are grouped together and referred to as “needle beds”. With the control of detection software, the detection points and signals can be programmed. In reality, only the probes of the test points needing testing are installed. While it is possible to test both sides of the circuit board simultaneously using the needle bed test method, during the circuit board design phase, all inspection points should be on the soldering surface of the circuit board. The needle bed tester is costly and challenging to repair. Depending on the specific application, probes are selected for different arrangements of needles.
A basic general-purpose grid processor consists of a drilled board with pins centered at 100, 75, or 50 mils. These pins act 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 perforated according to specifications will be placed between the grid and the circuit board to aid in the design of specific probes. Continuity detection is achieved by accessing the end points of the grid, defined as the x-y coordinates of the pad. Each network on the circuit board is tested for continuity, completing an independent test. However, the effectiveness of the bed-of-needle test method is restricted by the proximity of the probes.
With the introduction of surface mount technology, the packaging density of circuit boards has increased rapidly. Therefore, even for low-density, ordinary circuit boards, the automatic detection of circuit boards is not only fundamental but also cost-effective. In 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 discuss the needle bed test method.
Needle Bed Test Method:
In this method, a probe with a spring is connected to each detection point on the circuit board. The spring ensures that each probe exerts a pressure of 100-200g to ensure proper contact with each detection point. These probes are grouped together and referred to as “needle beds”. With the control of detection software, the detection points and signals can be programmed. In reality, only the probes of the test points needing testing are installed. While it is possible to test both sides of the circuit board simultaneously using the needle bed test method, during the circuit board design phase, all inspection points should be on the soldering surface of the circuit board. The needle bed tester is costly and challenging to repair. Depending on the specific application, probes are selected for different arrangements of needles.
A basic general-purpose grid processor consists of a drilled board with pins centered at 100, 75, or 50 mils. These pins act 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 perforated according to specifications will be placed between the grid and the circuit board to aid in the design of specific probes. Continuity detection is achieved by accessing the end points of the grid, defined as the x-y coordinates of the pad. Each network on the circuit board is tested for continuity, completing an independent test. However, the effectiveness of the bed-of-needle test method is restricted by the proximity of the probes.
