PCBA control panels may require complete or partial repair under the following circumstances:

1. The material model is wrong

2. Mispasting the polarity of materials

3. empty paste material is not empty paste

4. Temporary change of model

5. component damage

6. Poor welding

7. poor function & etc

Farway has a professional maintenance technical team, years of maintenance technical experience and professional maintenance equipment, can reduce unnecessary losses for you to the greatest extent.

PCBA repair process:

1. Visual inspection: it is mainly to check whether the defective PCBA has obvious bad appearance. Such as: short circuit, empty welding, lack of components, components of the reverse, wrong components of the damage, etc.

2, the measurement of the power supply: the main measurement power supply has no short circuit to the ground

3, power test: power after the use of test tools to check whether there is no adverse phenomenon

4, classified maintenance: according to the adverse phenomenon combined with the circuit schematic diagram for maintenance, and then summarize the rules, to develop the maintenance process or targeted SOP (operation instruction)

5. Self-check after maintenance: It is necessary to self-check the maintenance part after maintenance. Main inspection: short circuit solder bead tin slag and solder joint appearance, as well as the maintenance point around the components are affected

6, functional test: use test fixture or auxiliary function test tools to detect whether the board function is restored well

7, classification labeling: for the repaired board to do a good job of identification and maintenance records, unrepaired board also to do a good job of identification and maintenance records, and then in-depth analysis

8. Full inspection: Complete inspection of the appearance of the maintained products, cleaning and anti-static packaging.

7 methods commonly used in PCBA maintenance:

Based on the analysis and maintenance experience of PCBA defective products over the years, we generally summarize the maintenance methods into the following seven categories:

1. visual method

Visual is the basis of all maintenance. When a piece of bad PCBA is in hand, the first thing we need to do is to carry out a comprehensive appearance inspection of PCBA, to see whether there is broken wire, open circuit, short circuit, cold welding, missing parts, multiple pieces, wrong parts, kneeling and parts displacement, monument, anti-white, deformation or burned, etc., especially pay attention to whether there is tin on the back of PCBA? In addition, it also depends on whether the defective PCBA has been repaired, whether the BGA solder joint is regular, and whether there are traces of the soldering iron moving in other parts. Visual inspection is the first and very important step in maintenance analysis.

Many people are often ignored this, after a bad PCBA reach, can't wait to start the multimeter, oscilloscope and other detection tools constantly check to check, by the time we spent a lot of time to check the problem, only to find that the bad points as long as a little visual can easily solve, now regret it too late? Most long-term maintenance and F/A personnel have these experiences and lessons. In fact, some PCbas have been fixed for days without a clue. Eventually, often unconsciously, the problem is solved visually. Therefore, special attention should be paid to this point in the actual maintenance analysis to avoid more detours.

2. the comparative method

As the saying goes: No comparison, no difference. Comparison is also a maintenance method we often use. We tend to measure some signal or value deviation in the maintenance process, but are not sure if this is abnormal, then the best way is to take a good part against the control measurement, sometimes with samples or in order to get a stronger evidence, we tend to compare a dozen to a dozen.

The comparison can be divided into the following aspects:

1. According to the measurement method, it can be divided into:

A. Comparison of resistance measurements; B. Comparison of voltage and waveform measurements; C. Comparison of current current measurements.

2. According to appearance, it can be divided into:

A. Comparison of multiple pieces and missing pieces; B. Comparison of faulty parts; C. Comparison of different manufacturers for the same part

3. Functional tests can be divided into:

A. Comparison of functional tests of different stations B. Comparison of functional tests of good and defective products C. Comparison of functional tests of fixtures of different specifications; D. Comparison of functional tests of different external devices

Comparison is a shortcut that can help us find problems quickly. By comparing different maintenance methods, we can find the key to the problem in time and accurately.

3. touch method

Strictly speaking, touch method, also known as temperature sensing method, means that your hand can directly feel the temperature of the chipset or other components on the PCBA, and intuitively determine whether the PCBA is working properly.

▪ This method can be used for practical maintenance analysis and functional testing of production lines. During PCBA production, for those PCbas where the equipment is hot but functional testing is normal, we have an example of having the operator touch the equipment to determine the quality of the PCBA

▪ In the process of repairing and analyzing a broken PCBA, we often have this experience. At the moment, we can't find the real cause of some of the problems, but when our hands sometimes unconsciously touch some BGA or chip, we feel that they are hot and they heat up very quickly.

4. hand pressure method

In repairing some bad PCBA, mainly unstable PCBA, we may encounter some problems that cannot be measured when measuring the signal. At this point, we can manually press some chips on the PCBA, mainly the BGA closing element. Let's see if it's okay!

If it is good, we can say RedoKBGA or try to replace the chip. Manual pressing method is mainly suitable for BGAopen, cold welding or tin crack and other undesirable phenomena. Can be used for power test and normal resistance value test. Its advantage is that it can reduce the tedious steps of related measurement and maintenance, and greatly shorten the maintenance time. Manual pressing method is mainly suitable for BGAopen, cold welding or tin crack and other undesirable phenomena. Can be used for power test and normal resistance value test. Its advantage is that it can reduce the tedious steps of related measurement and maintenance, and greatly shorten the maintenance time.

Manual pressing method also has certain stress. For a MATURE maintenance analyst, THE force should be appropriate when the PCBA is pressed by hand. Do not exert too much force, do not lift one end of the PCB, and then press the BGA with your hand in case the PCB is powered off or disconnected.

When testing for cold welding during BGA power-on, the top of the BGA must be pressed by hand to achieve better results. When a signal is connected between two BGA, and we measure that its resistance (diode value or resistance value) is too large, and there are no other components between the lines for us to open, how do we determine which BGA is poorly welded? At this point, we can first take a simple and effective approach, which is to manually press two related BGA. When we pressed BGA, its resistance returned to normal, indicating the presence of poor welding.

▪ Press repeatedly in different directions to get the result. Once or twice may not work, but don't be discouraged. Try and press it many times, and you'll soon find the answer.

▪ It is worth reminding that some BGA open or cold welds can be determined by manual pressure, but not all open or cold welds can be determined by manual pressure.

5. open circuit method

Open circuit method is a common method to measure the resistance of PCBA components. The so-called open circuit method is to disconnect the line and check it separately. Usually used to judge cold welding, open circuit, short circuit of some parts or a point resistance value is too large or too small.

▪ In the process of disconnecting the circuit, we sometimes need to remove some resistor, inductor, triode or other components, and sometimes we need to pick up some chip pins. Eliminating the drain resistance near the chip to measure the upper limit signal is a typical application of the open-circuit method.

▪ It must be emphasized here that when some signals are connected between the BGA and there is no small part in the middle of the line for us to disconnect, we must not cut the PCB wiring to find the unauthorized fault point.

▪ Because the company has strict appearance requirements for PCBA products, not only did not troubleshoot, but also spent a lot of time, took many detours, and sometimes even scrapped PCBA because of too many BGA reworks.

▪ It is not uncommon for the examples above to be popular in routine maintenance operations.

▪ As an excellent maintenance analyst, every step requires rigorous logical thinking ability and accurate judgment, clear mind, clear thinking, orderly analysis, to achieve twice the result with half the effort.

6. decontamination method

▪ As the name suggests, remove dirt from PCBA?

There are some adverse phenomena on PCBA, such as large battery leakage or poor function test of other external equipment, etc. Before measuring or replacing parts, we can visually see the suspected places have Wuxi slag and other sundries, etc., and clean them when necessary. This trick will have a strange effect on some adverse phenomena.

7. the replacement method

▪ The replacement method we refer to refers to the repair method when the resistance, voltage, and waveform measurements are not valid, because not every defective PCBA piece can be visually detected with the detection tool.

▪ The substitution method also has certain principles. We can decide which one to replace first and which one to replace later according to our understanding of various PCBA and maintenance experience. Secondly, the measurement of some key signals can also be used as the basis for our replacement.

▪ In practical maintenance, our replacement is a typical application of the replacement method for defective PCBAs that are currently difficult to find.

As mentioned before, we only use the replacement method when we really can't find the problem point, but in the actual maintenance, we should not replace the BGA or other chip at any time without thoroughly checking the relevant line because of laziness or temporary negligence. This usually affects its function.

▪ In addition, too much magnetic flux can cause the battery to leak too much current. Of course, some excess flux can be detected with a multimeter. We should not forget this during the maintenance period.