In-Circuit Test (ICT) is a standard test method to check the PCBA manufacturing defect and poor component by testing the electrical performance and connections of circuit components. It mainly checks the in-circuit individual components and the open and short circuit conditions of each circuit network. It has the characteristics of simple operation, fast and rapid, and accurate fault location.A good electronic engineer will pre-consider test point when designing a PCB.
The flying probe ICT only performs static testing, and the advantage is that it does not need to make fixtures, and the program development time is short.
ICT Needle-bed can test analog device functions and logic functions of digital devices and has a high fault coverage rate. However, special needle-bed fixtures need to be made for each type of single PCB board, and the fixture production and program development cycle is long.
The Function and Benefits of ICT In-Circuit test
1.General functions of ICT:
(1) It can detect all the parts on the assembled circuit board in just a few seconds,such asresistors, capacitors, inductors, transistors, FETs, LEDs, ordinary diodes, stabilized diodes, optocouplers, ICs, etc. It also checks whether the part works within the specifications of the design.
(2) It can determinethe PCBA manufacturing process defects in advance, such as short circuit, open circuit, missing parts, reverse, wrong parts, empty welding, etc.Then it provides feedback to the improvement of the process.
(3) The faults mentioned aboveor test resultscan be printed out, including the location of the fault, the standard value of the part, and the test value for reference by the maintenance personnel. It can effectively reduce the personnel's dependence on product technology. Even if the personnel is not experienced with PCB circuits, they are still able ability to contribute.
(4) It can determinethe failedtest, and the production management personnel can analyze the information to determine the causes of defects, including human factors. This is so that they can resolve, correct and improve the circuit board manufacturing and quality capabilities.
2、ICT special functions:
- Electrolytic capacitor polarity test technology:
The electrolytic capacitor is reversed, and the missing parts are 100% testable
Parallel electrolytic capacitors are reversed, and the missing parts are 100% testable
The working principle of electrolytic capacitor polarity test technology:
1.1 It is to use the third pin to apply a trigger signal to the top of the electrolytic capacitor and measure the response signal between the third point and the positive or negative terminal.
1.2 After calculating with DSP (digital signal processing) technology, it is converted into a set of vectors through DFT (Discrete Fourier Transform) and FFT (Fast Fourier Transform). The resulting response signal is converted from t(time) domain (oscilloscope signal) to f(frequency) domain (spectrum analyzer signal) vector group.
1.3 Getting a set of standard vector values through learning, and then the measured value of the DUT (Device Under Test) is compared with the original standard value through Pattern Match (feature recognition and comparison technology) to determine whether the polarity of the test object is correct or not.
Pattern Match is used in applications such as fingerprint recognition, counterfeit currency recognition, retina recognition, etc.
Benefits of ICT (In-Circuit Test)
- Increased output: The ICT has rapid detectionspeed in the circuit tester. For example, the PCBA boards with 300piece components are tested in about 3 seconds, which significantly shortens the manual testing time, and the output can be greatly improved.
- Cut costs:
- Simplify maintenance work, speed up maintenance, reduce headcount, and reduce maintenance costs.
- Reduce the cost of components damaged by human errors.
- Reduce inventory of spare components.
- Improve the first-time yield rate of PCBA products: Provide a large amount of statistical data so that the production manager can supervise, adjust and manage the PCBA production process in time.
- Reduce human errors: The ICT in-circuit tester is accurate inerror detection, avoiding human errorsin determining the failure.
- Reduce operationcosts: The ICT in-circuit tester tests the entire board at one time, or it can test multiple boards simultaneously, with only one operator.
- After the PCBA product is tested by ICT. All hidden problems are removed for the later functional test.
- The modern PCBA production line, with ICT testing, will produceexcellent product quality.
ICT Testing Principle
- Open/Short test：Put one sample PCBA board on the test fixture. Do Pin to Pin learing（learning standard20Ω），compare when testing R<10Ω as Short and R>80Ω as Open.
That is Short:10Ω, Lr:20Ω, Open:80Ω. This standard is the system default setting and can be changed if needed.
There are two types of circuits that are helpful in electronic measurement: 1. To generate measurement parameters (voltage and current). 2. To control the existing voltage and current in the circuit.
When measuring resistance Rx with multimeter
If the potential Va at point A is sent to point G, let Vg=Va Ir1=(Va-Vg)/R1
∴Ir1=0 Is=Ix ∴ Rx=Vx/Is
Resistance measurement is the extrapolation from voltage and current measurements. The ohmmeter itself must provide an excitation source for the boards under test. The resistance can be measured without being part of the circuit. Suppose the resistance is part of the circuit. In that case, other voltage or current sources must be removed, and the power supply or battery must be turned off or disconnected from the circuit. Otherwise, the current or voltage will have the reading incorrect.
1. Resistor R（MODE D1,D2）
DC constant current source: According to Ohm law: V=IR，we get Rx=Vx/Is。
Therefore, Rx can be calculated by measuring the AB terminal voltage Vx.
(Constant current range: 0.1UA-50MA)
Resistor R/C（MODE V5,CV）
DC constant voltage source: According to Ohm law: V=IR，we get Rx=Vs/Is=0.05V or 0.1V/I
Therefore, if Ix is obtained, the Rx value can be calculated.
Resistor R/L（MODE P1、P2、P3、P4、P5）
Phase method test: AC voltage must Vs, assisted by phase method Rx=1/|Y`|Cosθ
Resistor R （MODE XR）
25V voltage source, measure the resistance above 1M
2. *Capacitor C （MODE A1 A2 A3 A4 A5）
AC constant voltage: AC voltage must be Vs, Vs/Lx=Zc=1/2πfCx
*Capacitance C/R (MODE P1 P2 P3 P4 P5)
Phase method test: |Y`|Sinθ=|Ycx|, ie ωCx’Sinθ=ωCx
Get: Cx=Cx’Sinθ (Cx’=Ix’/2πfVs)
*Capacitance C 3UF or more large capacitance (MODE DC)
DC constant current: C=ΔT/ΔV*I
*Inductance L (MODE A1 A2 A3 A4 A5)
Vs/Ix=Zl=2πfLx get: Lx=Vs/2πfIx
Phase testing ：|Y`|Sinθ=|Ycx|,即Sinθ/ωCx’=1/ωCx get：Lx=Lx’/ Sinθ ( Lx’=Vs/2πfIx’)
3.*Diode, Zener tube, Transistor Bc, Be, IC
A diode is a two-terminal component. When it is reverse biased, the anode voltage is negative relative to the cathode, and it has a high resistance. When it is NPN, it presents voltage drop and low resistance. The drop of forward voltage is related to the type of diode, usually less than 1V. Silicon: 0.6v-0.7v, germanium tube: 0.25-0.4v, Schottky block type: 0.4-0.5v, LED: 1.5-2.5v.
When measuring the diode, Vs should be bigger than the forward voltage drop of the diode. But it should not be too big to avoid excessive voltage or diode damaged by the current. NPN test: The general voltage source is 2.2V, and then measure its voltage. Forward direction: about 0.7v, reverse direction: 2.2v. The forward voltage drop of a diode is related to the diode type and is usually less than 1V.
Silicon: 0.6v-0.7v, germanium tube: 0.25-0.4v, Schottky barrier type: 0.4-0.5v, LED: 1.5-2.5v.
IC test in ICT Test Technology
There are three methods to test IC in ICT test: IC clamping diode test, IC scan, and IC test jet. Among these three test methods, the IC clamping diode test is the most commonly used, and most of the tests have this function. The IC scan function is a test program developed by PTI to the blind spots in IC testing. The IC test jet is a test solution developed by Agilent TestJet Technology to solve the problem of SMD IC pin open in circuits. It is used for IC open joint test.
IC Clamping Diode Test
The IC Clamping Diode test method tests the low voltage function with each IC pin to the IC VCC PIN, or with each IC pin to the IC's GND PIN, or with the two adjacent IC pins as the two test points.
The test program is generated by the automatic learning method. When making a program, use the software IC's Pin Edit function to put into the corresponding probe number of each pin of the IC, and specify which PIN is VCC PIN and GND PIN
The test principle: Test according to the protection diode of each pin in the IC manufacturer's footprint to GND/VCC, which can assist in the IC empty welding and reverse test.
IC SCAN technology checking SMD IC pin open circuit (PIN OPEN) method because each pin is tested by the three pins of the IC, so even the pin on the Bus can also be checked.
Its principle as shown in the figure:
step 1: A= --0.9v B=0v measure current,get: I1=I3+I4
step 2: A= --0.9v B= --1.2v Measure current, get: I2
step 3: I=I1-I2 I>0 get Good I≤0 get Bad
- Point B must be an independent pin
- Given voltage and measure current
- Digital IC can be measured
- The cut-off voltage of the two ICs is different and cannot be tested.
IC Test Jet
In order to conduct the test, the IC test jet uses the sensor plate on the fixture to press on the IC; the sensor plate's shape and area are the same as the IC shell. Then use the capacitance between the sensing board's copper foil and the IC foot frame to check the open circuit of the pin. The system sends a 200mV, 10KHz signal from the test point to the IC pin. The signal passes through the capacitive coupling between the IC frame and the sensing board, then through the amplifier on the sensing board. Go to the 64 channel signal conditioning card to select and amplify the signal, and finally connect to the test jet system to measure the signal strength. If the IC pins have open, as the signal could not be detected, the system will know that it is an open circuit. The PTI816NT ICT system is equipped with this technology, which significantly improves the detectability rate of digital circuit boards. Computer motherboard, adapter card, fax machine, and modem board can all get satisfactory test results. Agilent Testjet Technology can also detect the open circuit of various socket pins, whether it is Insertion type or SMD type. As shown below:
Judging from the current application situation, test methods that combine two or more technologies are becoming a development trend.
Different ICT testing technologies have advantages and disadvantages. By combining IC clamping diode test and IC scan technology, they do not need additional test accessories. IC scan is a free additional function of PTI and not affected by IC packaging/height and can test the parallel connection of ICs, especially for IT products such as motherboard BGA, sound card, display card. On the other hand, IC scan and test jet technology are mainly aimed at SMD IC testing its empty solder, cold solder, etc. IC test jet confirms whether the component exists, but it cannot confirm whether the components, directions, or values are correct. Using two or more test methods can reduce the ICT test failure rate.
2．Hardware Structure and Functions
The PTI816 series measuring board use a four-layer board structure, they are:
DC Board: DC signal source, measuring resistance, diode, triode
AC Board: AC signal source, measuring capacitance and inductance
SYS Board: Control and conversion of input and output signals
IC Scan Function Board: System self-check, IC scan function, test jet function test
- Relay Board: 4 layer board, using Reed Relay, with low internal resistance, low stray capacitance, high voltage,high current resistance, etc.
System self-diagnosis and debug function
TESTSELF.STD is a system self-test program, which includes some resistance, capacitance, and inductance.
*If the self-inspection finds that the resistance test or the voltage of 1V, 4V, 8V, or 24V failed, it means that the DC board is damaged.
*If there is a problem with a single resistor, it means that a certain gear on the DC board is not functioning properly.
*If the capacitor or inductance is poor in self-check, the AC board is damaged. If a certain capacitor or inductance is bad, the corresponding gear of the AC board is broken.
*If the SYS Board is damaged, all component tests will fail.
- DEBUG function (switchboard self-test)
When Relay Board self-checking, “MPX OK” will be displayed on the fluorescent screen. Otherwise, it will show that the corresponding switchboard's relay board is broken, such as: Open or Short.
If one or two abnormalities are found above, please make necessary relevant records and notify PTI as soon as possible.
Appendix 4: Ceramic capacitor error:
F：±1% R：-20% +100%
G：±2% S： 0% +20%
H：±2.5% T：-10% +50%
J：±5% Z：-20% +80%
★ Debug Sequence of Debug program:
- Fixing fixture: Turn off the photoelectric protection switch and fix the fixture on the press. Note-①The cylinder stroke makes the probe pressed down by 2/3. ②When a double-sided test fixture is fixed on the upper mold, switch the main screen to the part editing screen.
Then turn on the photoelectric protection switch.
- Cable connection: Connect the relay board and the fixture. Note: The flex cable corresponds to the horn of the fixture.
- Read the program: Put the test program in the disk under C:\COPY A:\ *.* C:\data directory, enter the test system,and call-out the program. Note: Programs include XX.dat, XX.pin, and XX.nal. (Main screen-L).
- Open/Short learning: Take a good product board and place it on the fixture for Learning. Note: OPS Delay is 120 or more. (Main screen-L).
- Sort: Enter EDIT (COMPONENTS) and sort by the actual value. Jumper-resistance-capacitance-inductance-diode-three-pole-IC; this sorting method is stable and fast during testing. (ALT+S).
- Scan: Program scan (SCAN) Press End Ctrl+F9 under Components.
- Components Debug.
- Learn IC: IC Clamping Diode（ALT+I）,IC_SCAN(ALT+W),IC TESTJET(ALT+X).
- Save: To save the program, pressF3.
Why Debug? When the new program is in actual SCAN, due to the selection of signal, the influence of component circuit or loop, and the error of the test pin number, few steps will be bad (the measured value exceeds ±%).
R debugging: According to the size of R, the system automatically adjusts the value of the test current. (0.1UA-50MA)
F9: Single-step debugging ALT+F9: Whole page debugging F5: Swap AB point
F10: Automatic Guarding ALT+H: View series components
ALT+J: View parallel components, select corresponding MODE and AB points
R/C: CV V5 and Dly(TM)
R/D: D2 V5
R/R: STD value is the parallel resistance
R/L: P1, P2, P3, P4, P5; According to Zx=2πfL, when L is constant if f is bigger, Zx is larger, and the influence on R is smaller.
C debugging: 3uf to 300uf, the system signal source is both AC and DC, above 300uf is DC Mode, small capacitors below 470pf are A4 A5 and OFFSET, 470pf to 3uf A3 A2 A1
F9: Single-step debugging ALT+F9: Whole page debugging F5: Swap AB point
F10: Automatic Guarding ALT+H: View series components
ALT+J: View parallel components, select the corresponding MODE and point A and B
C/C: STD value is the parallel capacitance value
C/R: A1, A2, A3, A4, A5; According to Zc=1/2πfC, when C is constant, the higher f is, the smaller Zc is, and the smaller the influence of R is.
C/L: P1, P2, P3, P4, P5; According to Zx=2πfL, when L is constant, if f is higher, Zx is larger, and the influence on C is smaller.
C/D: DC AB position A1, A2, A3, A4, A5 can conduct a good test.
D, Q, IC debugging: F9: single-step debugging ALT+F9: full page debugging
F5: Swap point AB
Forward: about 0.7V (NPN) Reverse: more than 2V (reverse cut-off)
D/C: LV add voltage and Dly
D/D: In addition to the forward conduction test for CM, a current test is also required.
Zener debugging: ACT value is bigger than Zener breakdown voltage +30%- +50%. If the test does not show the breakdown voltage, you can increase the gear and add Dly, and the Zener of 10V-48V can use HV.
The ce pole of Q: Need to confirm the type of Q (NPN, PNP), point A is the same (NPN), and point B is the same (PNP)
In order to make ce extremely saturated and conductive, the bias voltage of NPN is 0.6v-1v, and the bias voltage of PNP is 2.5v-1.8v. The reverse cutoff is above 0.5v (otherwise, adjust the ACT value).
Special test method:
Voltage regulator 7805:
Small resistance four-wire measurement: 1. When measuring minimal resistance, the resistance of the probe and the cable may introduce significant errors. The current Is flows through these stray resistances and generates a voltage across the resistance. Because the voltmeter contains R1 and R2 voltage in the measurement, the stray resistance added to the unknown resistance Rx will cause errors.
- The 4-wire ohm technology uses two additional test probes to avoid this error.The current Is flows through a set of separate probes to the unknown resistance. These probes/wires also have stray resistance and flow through the unknown resistance Rx. The current is a constant current source and remains constant. The other two test pins are the voltmeter test probes, which monitor the voltage on the unknown resistance, so there is no voltage drop at both ends. There is no current that flows through the two test pins. Therefore, the voltmeter can accurately test the value of Rx.
Common ICT misjudgments
1.ICT blind spot:
- Special IC - Some ICshave no protection diode for GND and VCC
- Single point test - Such as power strips, sockets, and individual components at a single test point
- More than ten capacitors in parallel - Show the accuracy of the capacitor for adjustment. See Attachment 4
- Parallel a large resistance that is more than 15 times the small resistance
- D/L or below D/10Ω, D is not measurable
- Parallel jumper
- IC internal function test
- Insufficient press stroke. Probe press-in range is 2/3
- The PCB board registration mast is loose, causing the probe to deviate from the pad.
- Test points on PCB, bare copper board, organic solderable preservative, flux, label, soldermask not opened, bad tin
- Poor PCB manufacturing process: If the board is not washed, the probewill havepoor contact due to excessive rosin
- Poor probe such as passivation of the needle, aging, high impedance, etc.
- Component manufacturer changessuch as small capacitorsand IC test jet can increase ±% and change test jet value
- ICT failure
ICT Equipment and Technology
The manufacturer of ICT equipment
Different manufacturers: Agilent Technologies, Teradyne, POSSEHL, SAMSUNG(FARA), T2000, GW, SEICA, WINCHY, TAKAYA, Check Sum (USA), Hioki, IFR, Takaya (Japan), Tescon, Okano(Japan), Rohde & Schwarz, Scorpion, Shindenski, SPEA, Tecnost-MTI, Testronics, SYS (Taiwan Series), Tr, WK Test, JET, Schuhll, Viper, TTI, SRC, Hong Kong Concord, etc. have applications in China.
Agilent hp3070, Teradyne, and Winchey have the highest market recognition among them.
The flying probe ICT only does static testing. The advantage is that no fixtures are required, and the program development time is short. Needle-bed ICT can test analog device functions, digital device logic functions, and a high fault coverage rate. However, special needle-bed fixtures must be made for each type of single board, and the fixture production and program development cycle is long.
Scope and characteristics: Check the electrical performance of in-circuit components and the connection of the circuit network. Firstly, it can quantitatively measure resistance, capacitance, inductance, crystal oscillator, and other devices. Secondly, it can conduct functional tests on diodes, triodes, optical couplings, transformers, relays, operational amplifiers, power modules, etc. Lastly, it could also conduct functional tests on small and medium-sized integrated circuits, such as all 74 series, memory, common drive, exchange, and other IC. It discovers manufacturing process defects and poor component by directly testing the electrical performance of online devices. It could check the component value out of tolerance, failure or damage, program error for memory parts, etc. For PCB & PCBA manufacturing technology, faults such as solder short circuit, wrong component install, reverse, missing, pin upturn, false soldering, and PCB circuit short and open can be found.
The test fault is directly located on the specific component, device pin, and network point, and the fault location is accurate. Repairs do not require much professional knowledge. Automated testing with program control is simple to operate and quick to test. The test time for a single board is generally from a few seconds to tens of seconds.
Importance: In-circuit testing is usually the first testing process in production, reflecting the manufacturing status, and is beneficial to PCB process improvement and upgrade. The faulty boards tested by ICT have accurate fault location and convenient maintenance, which can greatly improve production efficiency and reduce maintenance costs. Its specific test items are one of the important test methods for modern mass production quality assurance.
With the development of modern PCBA manufacturing technology and large-scale integrated circuits, it often takes a lot of time to write vector test programs for component boards. For example, the 80386 test program took nearly half a year of a skilled programmer to develop. A large number of SMT applications have made the fault issue of components pin open circuit more prominent. To this end, for each company's non-vector testing technology, Teradyne launched MultiScan, and GenRad launched Xpress non-vector testing technology. Thus, companies develop non-vector testing technology, Teradyne launched MultiScan; GenRad launched Xpress non-vector testing technology.
2.1 DeltaScan simulation junction test technology
DeltaScan uses the ESD protection or parasitic diodes of almost all digital device pins and most mixed-signal device pins to perform simple DC current tests on independent pins of the device. When the power of a certain board is cut off:
1 Apply a negative voltage to the ground at pin A, and current Ia flows through the NPN diode of pin A. Measure the current Ia flowing through pin A.
2 Keep the voltage of pin A, apply a higher negative voltage to pin B, and current Ib flows through the NPN diode of pin B. Due to the current sharing in the common substrate resistance from pin A and pin B to the ground, the current Ia will decrease.
3 Measure the current Ia flowing through pin A again. If Ia does not change (delta) when voltage is applied to pin B, there must be a connection problem. The DeltaScan software does a comprehensive analysis of the test results obtained from many possible pins on the device to obtain an accurate fault diagnosis. Signal pins, power and ground pins, and substrates all participate in the DeltaScan test. This means that DeltaScan can also detect missing components, reverse, and disconnect solder wires in addition to pin disconnection. GenRad type test is called Junction Xpress. It also uses the IC's diode characteristics, but the test is achieved by measuring the diode's spectral characteristics (second harmonic). DeltaScan technology does not require additional fixture hardware, becoming the first technology to do so.
2.2 FrameScan capacitor coupling test
FrameScan uses capacitive coupling to detect pin disconnection. There is a capacitive probe on each device. The signal is excited at a certain pin, and the capacitive probe picks up the signal.
1 The multiple switch boards on the fixture select the capacitive probe on a specific device.
2 The analog test board (ATB) in the tester sends an AC signal to each pin, under test, in turn.
3 The capacitive probe collects and buffers the AC signal on the tested pin.
4 ATB measures the AC signal picked up by the capacitive probe. If the connection of a specific pin to the circuit board is correct, the signal will be measured. If the pin is disconnected, there will be no signal.
GenRad this kind technology is called Open Xpress. The principle is similar.
The fixture for this technology requires sensors and other hardware, and the test cost is slightly higher.