A newly designed pcb circuit board after SMT, wave soldering or manual soldering into PCBA, is the first step. However, from PCBA assembly to the final delivery of the factory mass production, the middle still needs to go through a series of testing and verification work. Many young electronic engineers are not clear about the debugging steps and specific requirements of each stage of PCB assembly and electronic products, which often lead to inefficient development and debugging, or even damage the circuit boards to be tested. What is even more frightening is that the design with functional or performance defects will be transferred to the stage of mass production, causing huge losses to the company. Based on years of practical experience, Topscom summed up nine steps from PCBA to product stereotyping, and efficiently completed the research and development of a variety of electronic products to mass production.
The first step is visual inspection.
PCBA, experienced engineers who have just been mounted and delivered to electronic engineers can quickly find many design, material and process problems through visual inspection, which can save a lot of follow-up debugging time.
1.1. Carefully compare the circuit diagram, check whether the version of the schematic diagram, PCB diagram and BOM and the physical object you have got match, and confirm whether the important components of PCBA actual welding match with the circuit diagram, etc.
1.2 check whether there is tin bead tin slag on the board, continuous welding virtual welding, whether there is obvious missing welding of missing parts; gently pull out the components with relatively large head, especially electrolytic capacitors, high-power inductors and hand inserts, and carefully observe whether the return position is accurate and whether the solder joint is firm.
1.3 pay attention to check the arrangement of the power cord, the important IC mounting direction, the diode AK direction, the polarity of the polar capacitor, and the notch direction of the connector.
Second step impedance test.
This step is relatively simple, but it is extremely important, and many serious problems are caused by ignoring this step. Please verify the polarity and voltage of the power supply to be loaded repeatedly, and check whether there is a short circuit between each input and output power supply and the ground through the multimeter, whether there is any obvious impedance anomaly, and must not take any chances if there are any anomalies.
The third step is power-on check.
With nervousness, I guess you can't wait to power up your circuit board. All right, you can power up, but you have to power up correctly with the preparation for heroic sacrifice at any time. Connect the negative pole of the power cord to the negative pole of the experimental power supply, and after confirming that the output voltage of the experimental power supply is correct, gently lap the positive pole of the power cord to the positive pole of the experimental power supply terminal, do not rush to observe waveforms and data with the instrument, only care about whether there are abnormal phenomena in the moment when PCBA is powered on, such as smoke, fire, electric spark, abnormal smell, device bursting, etc., as shown in figure 3. If there is anything abnormal, remove the power cord immediately, return to the first step to troubleshoot the problem, and wait for the problem to be identified and dealt with before redoing this step. After confirming that there is no abnormality, you can formally power on, and after observing for a period of time, no abnormality or obvious hot IC can be found, and then you can move on to the next step.
Step 4 static test.
After the PCBA is officially powered on, follow the following steps to conduct a static test against the hardware design specification.
4.1 Measurement of working voltage and working current.
The test of DC voltage is very convenient and can be measured directly. However, the measurement of current is not very convenient, and two methods are usually used to measure it. If the circuit has a test point on the printed circuit board, it can be connected to the ammeter to measure the current value directly, and then connected with solder. If there is no test hole, the DC voltage can be measured, and then the DC current can be calculated according to the resistance value. For circuits with multiple power supplies, it is also necessary to test the power-up timing of each power supply.
4.2 processor minimum system default state test.
It is necessary to confirm the polarity and waveform of the processor reset level, the frequency of the crystal oscillator circuit, the state of the input configuration pin, and the initial state of the output control pin.
4.3 initial state test of logic circuit.
Focus on whether the chip selection signal, the enable signal and the default state of the configuration pin meet the requirements. The default state of the DIR_485 pin is low, as shown in figure 6.
4.4 Analog Circuit operating Point Test.
DC static operating points such as amplifiers, transistors and MOS transistors need to be tested and optimized. For example, the resistance values of R1 and R2 in figure 7 need to be calculated according to the parameters of the MOS tube and adjusted according to the measured results.
The fifth step is function debugging.
This stage usually requires software-driven cooperation, need to use a variety of professional instruments and equipment, such as signal generator, logic analyzer, oscilloscope, spectrum analyzer, electronic analog load and so on.
5.1 break through the processor debugging interface to download, run and output software programs.
5.2 verify the human-computer interaction function, and the information indication function is normal.
5.3 through program control, drive the digital circuit to observe whether the output signal waveform, amplitude, pulse width, phase and dynamic logic relationship meet the requirements. Verify logic control and communication interface functions, input status is correct and output state is controllable.
5.4 adjust the AC path elements of the analog circuit, such as capacitance, inductance, etc., so that the waveform, amplitude, frequency and other parameters of the AC signal meet the design requirements.
5.5 input single step signal to test whether the logical relationship of the state change of the circuit meets the requirements.
5.6 verify that the drive circuit is working properly under no-load or light load conditions.
5.7 functional debugging reports shall be submitted after all functional debugging is completed.
Step 6 performance test.
After the circuit has been dynamically debugged and normal, the required technical specifications can be measured. Such as transmission speed, bit error rate, wireless transmission distance, signal-to-noise ratio and so on, test and record the test data, analyze the test data, and finally make a test conclusion to determine whether the technical specifications of the circuit meet the design requirements. If there is a discrepancy, the problem should be carefully checked, generally adjusting and changing some component parameters or software configuration. If it still fails to meet the requirements, a certain part of the circuit or configuration should be modified, or even the whole circuit should be re-modified. Therefore, it is required that in the whole process of design, we should be serious and meticulous, and consider the problem more carefully.
Step 7 Conformance Test.
After performance testing and confirming that the design requirements are met, at least three functional and performance consistency tests need to be carried out according to the actual situation, and the voltage, current, delay and signal waveforms should be compared and tested. if there is an obvious deviation, we must not be taken lightly, and we should carefully analyze the defects that may exist in the design, materials, processing technology or debugging and testing scheme. As shown in Table 3, we can analyze whether there is an occasional problem or a batch problem.
Step 8 systematic joint adjustment.
The PCBA which has passed the conformance test needs to be installed and fixed in the whole system for system joint debugging. In principle, it is also necessary to carry out system-level conformance testing.
The most common problems in the process of system joint adjustment are the interference of PCBA and structure, the influence of the position of wireless communication antenna on communication performance, the decline of performance caused by the deterioration of heat dissipation conditions, the decline of function or performance caused by communication bit error rate, the influence of audio and video part by box, motor blocking or overheating protection caused by insufficient load capacity, various anomalies caused by insufficient power supply capacity of the system, and so on. Due to the wide variety of electronic products, it needs to be carefully checked in combination with the system block diagram. The system block diagram of a product is shown in figure 9.
Step 9 type test.
Type test is an important link in the R & D stage of electronic products, the key node of the product from R & D to production, and also an important basis for whether the product can be finalized. The contents and requirements of specific tests vary according to the type and requirements of the product. However, the approximate scope is not much different from the test project, such as the type test outline of a product is shown in figure 10.
At present, electronic products are all-inclusive, integrated chips and functional circuits also emerge one after another, coupled with the high correlation of embedded system machinery, electronics and software, the difficulty of joint debugging from PCBA to system is gradually increasing. In addition, due to the fierce market competition and the continuous compression of the R & D cycle of electronic products, it puts forward higher requirements for the debugging ability and ability of electronic engineers in the whole process from PCBA to product stereotyping. Although the shape of electronic products and the specific application of electronic technology are different, the basic processes, steps and matters needing attention of debugging are highly interlinked. The nine-step debugging method can be used as a reference for electronic engineers in various industries.
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