This method is connected by a spring-loaded probe to each of the test points on the board. The spring has a pressure of 100 - 200g for each probe to ensure good contact at each test point, and the arrangement of such probes together is called a "needle bed". The detection point and the detection signal can be programmed under the control of the detection software. Figure 14-3 shows a typical needle bed tester structure where the tester can obtain information on all test points. In fact only those who need to test the test point of the probe is installed. Although the use of needle-bed test may be on both sides of the circuit board testing, when designing the circuit board, or should make all the test points in the circuit board welding surface. Needle bed tester equipment is expensive and difficult to repair. Needles are selected according to their specific application of different arrangements of the probe.
A basic general-purpose grid processor consists of a drilled plate with a center-to-center spacing of 100, 75, or 50 mils. The pins act as probes and are directly mechanically connected using electrical connectors or nodes on the circuit board. If the pads on the board match the test grid, the perforated polyester film 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 pad x-y coordinates. Since every circuit on the circuit board for continuity testing. In this way, an independent detection is complete. However, the proximity of the probe limits the effectiveness of the needle bed test method.