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 basic but also economical. In complex circuit board inspection, two common methods are the bed of needle test method and the double probe or flying probe test method. Today we will take about 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 makes each probe have a pressure of 100-200g to ensure good contact between each detection point. Such probes are arranged together and are called “needle beds”. Under the control of the detection software, the detection points and detection signals can be programmed. In fact, only the probes of the test points that need to be tested are installed. Although it is possible to test on both sides of the circuit board at the same time using the bed of needle test method, when designing the circuit board, all inspection points should be on the soldering surface of the circuit board. The needle bed tester is expensive and difficult to repair. According to the specific application of the needle, the probes in different arrangements are selected.

A basic general-purpose grid processor consists of a drilled board with pins centered at 100, 75, or 50 mils. The pins act as probes and use electrical connectors or nodes on the circuit board to make direct mechanical connections. If the pads on the circuit board match the test grid, then the polyester film perforated in accordance with the specification will be placed between the grid and the circuit board to facilitate the design of specific probes. Continuity detection is achieved by accessing the end points of the grid (which have been defined as the x-y coordinates of the pad). Since every network on the circuit board is tested for continuity. In this way, an independent test is completed. However, the proximity of the probe limits the effectiveness of the bed-of-needle test method.