There are several smta measurement methods
Typical non-vector testing methods are as follows:
(1) Semiconductor junction (PN junction) test
At present, when most digital integrated circuits are produced, they will consider the internal core functions and the protection factors of each signal input and output pin to ground, such as anti-static measures. In the semiconductor device design and forming process stage, the chip pins are paired. A specific PN junction and series resistance are formed between. Therefore, many professional testing technology development manufacturers based on the electronic characteristics of semiconductor PN junctions, that is, PN junctions of different materials will have their inherent turn-on voltage and current values, thereby realizing the electrical connection test of the digital integrated circuit pin welding effect.
Chip under test
In the PN junction test, the tested chip is connected to the working voltage source Vcc and grounded according to the normal working state, so that it is in a static working state. The test process is divided into three steps: First, a specific DC test voltage Vm is measured by a test probe. Applied to a certain chip pin, as shown in Figure 4.39, the voltage source connected to pin A is the negative electrode. At the same time, a current meter connected (connected in series with the test voltage source) measures the current value generated at this time; followed by another lead On the pin, a DC excitation signal (Vs) with a larger voltage value than pin A is connected through another probe. The voltage source connection method should be the same as the test voltage source. According to the basic principle of the circuit, this pin The potential of A is higher than that of pin B, and the current should flow from pin A to pin B, so the current value through pin A should be lower; finally the ammeter measures the current passing through pin A after the excitation voltage source is connected, if any The change indicates that the electrical connection between pin A and pin B is good. If there is no change, it is judged that there is a problem.
As mentioned above, through different test probes connected to the pin test points of the tested chip, the test voltage signal and excitation voltage source are moved one by one on each pin test point of the IC one by one, and then the entire chip pin The electrical connection performance is tested and judged. This kind of non-vector test is suitable for integrated circuits that are known to have such PN junction characteristics. The same working principle can also be suitable for other types of chips with similar structures. It can determine the connection between the internal pins of the chip and the lead frame.
The connection, the connection between the pad and the pin, the connection between the pad and the PCB wire, whether the test point matches the description of the circuit netlist, etc.
(2) Capacitance sensing test
The basic principle of this non-vector test is that under the excitation of a certain frequency AC signal, a certain capacitance effect will be generated between the component under test and the sensing device, and the excitation AC signal can be obtained through a movable or fixed capacitance sensing device , Through the test equipment measurement and comparison, to determine the electrical connection between the pin and the test path.
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The capacitance sensing test process can be briefly described as follows.
The first step: The test equipment passes the test probe that has contacted the test point of the device under test, and applies a specific frequency AC signal. The test signal frequency is usually 1.59Hz, 1.59kHz, 15.9kHz, according to the capacitor used The type and size of the sensing device and the characteristics of the tested object are automatically selected.
Step 2: Move the capacitance sensor device to the top of the pin of the device under test that is connected to the test signal, and pick up the coupling signal of the test signal through the capacitive coupling effect generated between the capacitance sensor and the device.
The third step: The capacitance sensor sends the detected signal to the signal filtering, detecting and amplifying circuit (usually a multi-channel signal board).
Step 4: The amplified and identifiable capacitance sensing signal is sent to the measurement circuit module (card) for measurement. If the expected test response signal is not found, it is judged as an open circuit.
Capacitive sensors can have several different types and placement positions in different test equipment. Double-panel testing is usually placed on both the upper and lower sides at the same time.
Figure 4.41 Application of capacitive sensing device
Capacitance sensing non-vector testing is the most effective for testing the solder open-circuit defects of analog and digital circuit devices.
(1) RF induction test
This non-vector testing method uses the electromagnetic field effect generated by the 200kHz-500kHz AC signal for device introduction.
For the detection of foot welding defects, the application device is similar to the capacitive induction test, which can generate a spirally distributed electromagnetic field that diffuses outward, as shown in Figure 4.42.
Switch conversion board
The radio frequency induction test process is divided into five steps: the first step, the test program controls the test switch conversion device to connect the radio frequency signal source to the electromagnetic signal initiating device; the second step, the radio frequency signal device sends a specific frequency excitation signal; the third step , The radio frequency initiation device forms an electromagnetic field effect located on the upper part of the device under test; the fourth step is to connect the constant current source through the test probe one by one; the fifth step, the test probe sends the electromagnetic field induced signal to the measurement circuit for testing, if not found The corresponding induction signal will be judged as an open circuit.
The above-mentioned three types of typical non-vector testing techniques can test device types and defect types, as listed in Table 4.4. The first method is to use capacitive coupling technology to measure the capacitance between each lead wire and the device lead frame; the second method is to measure the parasitic characteristic parameters of the transistor or diode for the pin protection of the digital circuit chip; the third method is to use The radio frequency electromagnetic field induces current in the circuit of the device, which is similar to the induction current of the primary side group of the transformer in the secondary side group. All three methods use test probes, which can also be used to test short circuits. Radio frequency non-vector testing technology is stronger than capacitive induction non-vector testing in defect detection ability. In addition to directly determining the effect of solder joints between device pins and pads, it can also determine the chip core and outer lead frame inside the device package through analysis The connection (bonding point) is good or bad.
Table 4.4 Comparison of three types of typical non-vector testing techniques
Defect type,
Test Technology X. Defect Type Applicable Device Conditions
IC polarity reverse socket or connector Open circuit IC open circuit Bonding Open circuit Device bad Single power supply and ground pin No special pin pair No static electricity Protection diode with grounding layer and heat dissipation layer No external lead frame with heat sink and fan
PN junction non-vector test 7
Capacitance sensing non-vector test V
RF induction non-vector test 7 x/
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In fact, no matter what kind of independent online testing technology, it can not cover all circuit assembly or design failures, and non-vector testing technology can not completely replace electrical connection testing and functional testing. This is due to the circuit design and layout
When organizing, there are always certain circuit layouts, device categories, packaging forms, etc., which make certain non-vector testing techniques impossible to apply. For example, capacitive technology can only detect devices with pin holders, while RF technology cannot detect connectors. However, each technology has its own strengths and different fault coverage; joint applications can provide the widest fault coverage, usually covering 90%-95% of surface assembly defects.
The emergence of non-vector testing technology has brought about a revolution in circuit board testing technology. Although it also has some shortcomings, such as the need to add test fixture accessories, test software needs to add corresponding automatic non-vector programming application capabilities, etc., with the development and maturity of this technology, it has fast test speed and simple programming. The advantages such as use, non-vector devices can be reused, etc. make it increasingly popular.
At present, the classification of non-vector testing technology is only based on the principle of technology application. The naming of its technology categories has not yet been unified. Many professional test equipment manufacturers have introduced various non-vector testing technologies with different names and names, but their essence is the previous The three typical technologies introduced above are based on the same principles, and their application methods have their own focus when implementing related tests. For example, Teradyne in the United States is widely used in its Z1800 series collectively referred to as the three types of MultiScan non-vector testing technology: DeltaScan corresponds to PN junction non-vector testing technology, FrameScan corresponds to capacitive induction non-vector testing technology, and WaveScan corresponds to radio frequency induction non-vector testing technology. Vector testing technology; for example, Agilent has the name TestJetVectorless Test EP; some manufacturers directly apply the non-vector test devices provided by other professional test equipment manufacturers, and rename them, such as OpenFix, OpensCheck, etc.
6. Comprehensive application of online testing technology
For any independent online testing technology, its testing scope and ability are still extremely limited for the complete testing of surface mount circuit modules. Comprehensive evaluation of the test capability of an online test system requires a clear test object, that is, the nature of the circuit module under test, test requirements, timeliness and many other factors. In addition to the basic technical indicators of individual test items, testable channels, test speed, and cost, The test coverage of assembly defects, defect diagnosis, data statistics, expansion, etc. are important indicators for measuring the technical level of the online test system. Among them, the index of test coverage includes the test technology application degree of online test equipment.
As an online test system for professional circuit assembly companies, the minimum requirement is to have a high assembly defect detection capability and data statistics function, that is, it can only be a conventional test probe contact test (circuit or component test). The comprehensive application of static electrical parameters, vector testing and simple non-vector testing technology), and non-contact electrical characteristic testing (such as non-vector testing technology) can meet the requirements of high assembly defect test coverage and high defect location.
Various types of non-vector testing technologies are not the same in several different types of testing equipment. The needle-bed online test has a more prominent advantage in this regard, especially the ability to use multiple non-vector testing induction devices of different specifications at the same time , And this type of device can be placed on the upper and bottom of the circuit component to be tested at the same time, as shown in Figure 4.44, with high positioning accuracy, a good guarantee for repeated test accuracy, easy programming, and high test efficiency. However, there are many requirements for configuration specifications and large costs.
(a) A non-vector test device installed on the top of the fixture; (b) a non-vector test device installed on the upper end of the fixed probe.
Compared with the needle-bed online test system, since the flying-probe online test equipment does not have a needle-bed structure, there are two situations in which it uses a non-vector test device: one is to use a magnetic or viscous base to be placed on the circuit component under test Below, it is like a bed of needle application; the other is directly installed on the probe arm. Of course, this kind of use needs to occupy a test probe position, and it needs to be moved to the required position with instructions during testing. Flying probe application non-vector testing technology has limited work efficiency and applicability. Generally speaking, only one test method with device coordination can be used to test a circuit component, and it will also affect other online test functions.
Of course, the stronger the comprehensive testing technology and testing capabilities of the online testing equipment, the more expensive it is. At present, there are many manufacturers of online test equipment, and the performance of the equipment is uneven, and the price ranges from tens of thousands of dollars to hundreds of thousands of dollars. Generally speaking, if the online test equipment only provides analog discrete component detection and general-purpose digital integrated circuit detection functions, it only costs less than 100,000 U.S. dollars. If the test equipment can provide boundary scan technology and non-vector detection technology, its price will increase rapidly. The increased fault coverage of test equipment and the increase in its price have increased almost exponentially. The hardware structure and the number of test points and test accuracy that can be provided by its expanded functions also have a great impact on the price.
