PCB Tech - Efficiently realize PCBA prototype to mass production

A newly designed circuit board becomes PCBA after SMT, wave soldering or manual soldering, which is the first step in the long march. However, from PCBA to final finalization and delivery to the factory for mass production, a series of tests and verifications are required in the middle. Many young electronic engineers are not clear about PCBA and electronic product system debugging steps and specific requirements at each stage, which often leads to inefficient development and debugging, and even damages the circuit board to be tested. What is even more frightening is that the design with functional or performance defects is transferred to the mass production stage, causing huge losses to the company. Based on years of practical experience.

First step visual inspection

The PCBA that has just been mounted and delivered to the electronic engineer is shown in Figure 1. Experienced 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 are consistent with the actual product you get, and whether the important components actually welded by the PCBA are consistent with the circuit diagram.

1.2 Check whether there are tin beads and dross on the board, continuous welding, and whether there are obvious missing parts and missing welding; gently pull out relatively large components, especially electrolytic capacitors, high-power inductors and hand plugs, carefully Observe whether the reconnecting position is centered accurately and whether the solder joints are firm.

1.3 Pay attention to check the power line arrangement, important IC mounting direction, diode AK direction, polarity of polar capacitor, and the notch direction of the connector.

Step 2: Impedance test

This step is relatively simple, but extremely important. Many serious problems are caused by ignoring this step. Please be sure to repeatedly verify the polarity and voltage of the power supply that needs to be loaded. Use a multimeter to check whether there is a short circuit between each input and output power supply and the ground, and whether there is obvious impedance abnormality. If there is any abnormality, it must be ruled out. lucky.

Step 3: Power on and check

Connect the negative pole of the power cord to the negative pole of the experimental power supply. 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. Don't rush to observe the waveform and data with the instrument. Only care about the moment when the PCBA is energized. Whether there are abnormal phenomena, such as smoke, fire, electric spark, abnormal smell, device burst, etc. The specific tragic symptoms are shown in Figure 3. If there is an abnormality, remove the power cord immediately, return to the first step to troubleshoot the problem, and perform this step again after the problem is found and resolved. After confirming that there is no abnormality, the power can be officially turned on. After observing for a period of time, no abnormality or obvious hot IC can be entered to the next step.

The fourth step static test

After the PCBA is officially powered on, follow the steps below to perform a static test according to the hardware design specification.

4.1 Working voltage and working current measurement

The test of DC voltage is very convenient and can be measured directly. The measurement of current is not very convenient, and two methods are usually used to measure it. If the circuit has test points on the printed circuit board, it can be connected in series with an ammeter to directly measure the current value, and then connect it 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

4.2 Processor minimum system default state test

Need 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 select signal, enable signal and the default state of the configuration pins meet the requirements. The default state of the DIR_485 pin as shown in Figure 6 is low.

4.4 Analog circuit operating point test

Need to test and optimize the DC static operating points of amplifiers, transistors, MOS tubes, etc. As shown in Figure 7, the resistance values of R1 and R2 need to be calculated according to the parameters of the MOS tube and adjusted according to the measured results.

Step 5 Function debugging

This stage usually requires software driver cooperation, and various professional instruments and equipment such as signal generators, logic analyzers, oscilloscopes, spectrum analyzers, electronic analog loads, etc. are needed.

Step 6 performance test

After the circuit is dynamically debugged, the required technical indicators can be measured. Such as the transmission speed, bit error rate, wireless transmission distance, signal-to-noise ratio, etc., test and record the test data, analyze the test data, and finally make a test conclusion to determine whether the technical indicators of the circuit meet the design requirements. If there is any discrepancy, you should carefully check the problem, usually to adjust and change some component parameters or software configuration. If it still fails to meet the requirements, some part of the circuit or configuration should be modified, or even the entire circuit should be revised again. Therefore, it is required to be serious and meticulous in the whole process of design, and to consider issues more thoroughly.

Step 7: conformance test

After performance testing and confirming that the design requirements are met, at least 3 or more functional and performance consistency evaluations are required according to the actual situation, and comparison tests for voltage, current, delay, signal waveforms, etc., if there are obvious deviations, you must not take it lightly. It is necessary to carefully analyze possible deficiencies in design, materials, processing technology, or debugging and testing programs. As shown in Table 3, it can be analyzed whether there is an accidental problem or a batch problem.

47 sets of product working current consistency test

The eighth step system joint debugging

The PCBA that has passed the consistency test needs to be installed and fixed in the whole system for system joint debugging. In principle, the system-level consistency test should also be carried out.

The most common problem in the process of system joint debugging is the interference of PCBA and structure; the influence of wireless communication antenna position on communication performance; The influence of the cabinet; motor stall or overheat protection caused by insufficient load capacity, various abnormalities caused by insufficient system power supply capacity, etc. Due to the wide variety of electronic products, it is necessary to conduct a careful investigation in conjunction with the system block diagram.

Ninth step type test

Type testing is an important link in the R&D phase of electronic products, a key node in the transition from R&D to production, and an important basis for product failure. The specific test content and requirements vary according to the type and requirements of the product.

Current electronic products are all-encompassing, and integrated chips and functional circuits are also emerging in an endless stream. Coupled with the high correlation of embedded system machinery, electronics and software, the difficulty of PCBA to system joint debugging is gradually increasing. In addition, due to the fierce market competition and the continuous compression of the electronic product development cycle, this places higher requirements on the debugging capabilities and capabilities of the electronic engineer from PCBA product finalization. Although the form of electronic products and the specific application of electronic technology are different, the basic process, steps and precautions of debugging are highly connected. The nine-step debugging method has a certain reference and reference for electronic engineers in various industries.