CN202018494U - Four-wire type PCB test fixture - Google Patents

Abstract

The utility model discloses a four-wire PCB test fixture, including a base, a pressure plate and a probe, wherein the probe includes a first terminal, a second terminal, a third terminal and a fourth terminal, wherein the first terminal and the second terminal are electrically connected to a constant current source of a test machine through a wire, and the third terminal and the fourth terminal are electrically connected to a constant voltage source of the test machine through a wire. By using the above four terminals, each test point of the corresponding PCB board has a completely independent current supply circuit and voltage measurement loop, and since the input impedance of the voltage measurement loop is extremely high, the wiring impedance and the contact impedance can be completely ignored, so that the resistance to be tested of the PCB board can be accurately measured, and the test accuracy can reach 1mΩ.

Description

Four-wire PCB test fixture

technical field

The utility model relates to the technical field of PCB testing, in particular to a four-wire PCB testing fixture.

Background technique

With the rapid development of electronic technology, the number of layers of printed circuit board (PCB) is getting higher and higher, the circuit density is getting denser, and the pad size is getting smaller and smaller. For PCB testing, the internal resistance of the components to be tested generally varies greatly. Sometimes it may be necessary to measure a component with an internal resistance of hundreds of megaohms, and sometimes it may be necessary to measure a component with a few milliohms. Moreover, there are many test points on the PCB board. High, so higher requirements are placed on PCB test fixtures.

Existing test fixtures can guarantee the measurement accuracy when the measured resistance value is large, but when measuring components with small resistance value, since the test probe line of the tester itself has a certain internal resistance, it is different from the resistance to be measured. When the value difference is small, the measurement value will have a large error, and the accuracy of the measurement cannot be guaranteed.

Under normal circumstances, the open circuit impedance of the PCB open and short circuit test parameter value is set to 25Ω. When the detected line resistance is greater than 25Ω, the tester judges it as an open circuit. When the detected line resistance value is less than 25Ω, the tester judges it as qualified. . Therefore, the tester cannot accurately test the actual resistance value of the line with a resistance value less than 25Ω, and the line below 25Ω becomes a test blind area. Especially for high-density mobile phone boards such as HDI, the requirements for copper thickness are strict. In actual production, some defects of PCB such as no copper in the hole, thin copper in the hole, holes in the hole, line gaps, etc. will affect the circuit. Resistance value; when the detected line resistance is less than 25Ω, when testing the above-mentioned defective PCB, the test result is qualified, resulting in the open circuit problem of these defective PCBs during use. Therefore, the existing test fixtures can no longer complete the complete test, and there are test blind spots.

Contents of the invention

The purpose of the utility model is to avoid the deficiencies in the prior art and provide a four-wire PCB test fixture with high test accuracy, which can detect various open circuit problems such as circuit gaps on PCB boards with circuit resistances up to 1mΩ.

The purpose of this utility model is achieved through the following technical measures:

A four-wire PCB test fixture is provided, including a base, a pressure plate and a probe, and the probe includes a first connection terminal, a second connection terminal, a third connection terminal and a fourth connection terminal, the first The connecting terminal and the second connecting terminal are electrically connected to the constant current source of the testing machine through wires, and the third connecting terminal and the fourth connecting terminal are electrically connected to the constant voltage source of the testing machine through wires;

When carrying out the PCB test, the input ends of the first connection terminal and the second connection terminal are connected to a constant current source, and the output ends of the first connection terminal and the second connection terminal are connected to the two ends of the resistance to be measured on the PCB board to form a current supply circuit;

The input ends of the third connection terminal and the fourth connection terminal are connected to a constant voltage source, and the output ends of the third connection terminal and the fourth connection terminal are connected to the two ends of the resistance to be measured on the PCB board to form a voltage measurement circuit.

Wherein, the base drill is provided with a drill hole corresponding to the probe, one end of the probe is connected to the elastic member in the drill hole, and the elastic member is connected to the testing machine through a wire.

Wherein, the constant voltage source is a power supply with a voltage of 50-250V.

Wherein, the constant current source is a power supply with a current of 10-100mA.

The beneficial effects of the utility model:

The four-wire PCB test fixture of the present utility model includes a base, a pressure plate and a probe, and the probe includes a first terminal, a second terminal, a third terminal and a fourth terminal, and the first terminal One connecting terminal and the second connecting terminal are electrically connected to the constant current source of the testing machine through wires, and the third connecting terminal and the fourth connecting terminal are electrically connected to the constant voltage source of the testing machine through wires; when carrying out PCB testing, all The input ends of the first connecting terminal and the second connecting terminal are connected to a constant current source, the output ends of the first connecting terminal and the second connecting terminal are connected to the two ends of the resistance to be measured on the PCB board to form a current supply circuit, and the third connecting terminal The input terminals of the connecting terminal and the fourth connecting terminal are connected to a constant voltage source, and the output ends of the third connecting terminal and the fourth connecting terminal are connected to two ends of the resistance to be measured on the PCB board to form a voltage measurement circuit. When the above four terminals are used for PCB testing, each test point has a current supply circuit and a voltage measurement circuit. The line impedance and contact impedance can be completely ignored, so that the resistance of the PCB board to be tested can be precisely measured, and the test accuracy can reach 1 mΩ.

Description of drawings

Utilize accompanying drawing to further illustrate the utility model, but the content in the accompanying drawing does not constitute any restriction to the utility model.

FIG. 1 is a schematic structural view of a four-wire PCB test fixture of the present invention.

FIG. 2 is a schematic diagram of the circuit principle of the four-wire PCB test fixture of the present invention.

Figures 1 to 2 include:

Base 1, pressure plate 2, probe 3, PCB board 4.

Detailed ways

The utility model is further described in conjunction with the following examples:

Embodiment 1 of the four-wire PCB test fixture of the present utility model is shown in Fig. Connecting terminal, the third connecting terminal and the fourth connecting terminal, the first connecting terminal and the second connecting terminal are electrically connected to the constant current source of the testing machine through wires, and the third connecting terminal and the fourth connecting terminal are connected to the constant current source of the testing machine through wires. The constant voltage source electrical connection of the testing machine.

As shown in Figure 2, R1, R2, R3, and R4 are feeder resistances, Rpcb is the resistance to be measured, I1 is the current of the current supply circuit, and I2 is the current of the voltage measurement circuit. When carrying out the PCB test, the input ends of the first connection terminal and the second connection terminal are connected to the constant current source, and the output ends of the first connection terminal and the second connection terminal are connected to two terminals of the PCB board 4 resistance Rpcb to be measured. The terminal constitutes a current supply circuit, the input ends of the third connection terminal and the fourth connection terminal are connected to a constant voltage source, and the output ends of the third connection terminal and the fourth connection terminal are connected to two terminals of the PCB board 4 resistance Rpcb to be measured. terminal constitutes a voltage measurement circuit.

When the above four terminals are used for PCB testing, each test point has a current supply circuit and a voltage measurement circuit. The current supply circuit and the voltage measurement circuit are completely independent. Because the input impedance of the voltage measurement circuit is extremely high, the The current I2 of the overvoltage measurement circuit is extremely small, approximately zero, and the cable impedance and contact impedance can be completely ignored, so that the resistance value Rpcb to be tested at the test point of the PCB board can be precisely measured, which solves the problem of the lack of copper in the hole of the PCB board. , Open circuit problems caused by defects such as thin copper in the hole, voids in the hole, and line gaps.

In this embodiment, the constant voltage source is a power supply with a voltage of 50-250V, the constant current source is a power supply with a current of 10-100mA, and the resistance value of the PCB board to be tested is 1mΩ-100Ω. The four-wire PCB of the utility model The test fixture effectively improves the test accuracy to 1mΩ.

In this embodiment, the base 1 is drilled with a hole corresponding to the probe, one end of the probe is connected to the elastic member in the hole, and the elastic member is connected to the testing machine through a wire.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model rather than limiting the protection scope of the utility model. Although the utility model has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should It is understood that the technical solution of the utility model can be modified or equivalently replaced without departing from the essence and scope of the technical solution of the utility model.

Claims (4)

1. A four-wire type PCB test fixture, including a base, a pressure plate and a probe, is characterized in that: the probe includes a first terminal, a second terminal, a third terminal and a fourth terminal , the first connection terminal and the second connection terminal are electrically connected to the constant current source of the testing machine through wires, and the third connection terminal and the fourth connection terminal are electrically connected to the constant voltage source of the testing machine through wires; When carrying out the PCB test, the input ends of the first connection terminal and the second connection terminal are connected to a constant current source, and the output ends of the first connection terminal and the second connection terminal are connected to the two ends of the resistance to be measured on the PCB board to form a current Supply circuit; the input ends of the third connection terminal and the fourth connection terminal are connected to the constant voltage source, and the output ends of the third connection terminal and the fourth connection terminal are connected to the two ends of the resistance to be measured on the PCB board to form a voltage measurement circuit . 2. The four-wire PCB test fixture according to claim 1, wherein the base is drilled with a hole corresponding to the probe, and one end of the probe is connected to the elastic member in the hole. connected, the elastic member is connected with the testing machine through wires. 3. The four-wire PCB test fixture according to claim 1, wherein the constant voltage source is a power supply with a voltage of 50-250V. 4. The four-wire PCB test fixture according to claim 3, wherein the constant current source is a power supply with a current of 10-100mA.

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