How to inspect the manufacture and assembly of printed circuit boards

.For customers who buy printed circuit boards, the most taboo thing for them is to change suppliers at will, which is not only time-consuming but also expensive. Prototype pcbs are generally purchased before mass manufacturing, and mass production will begin only after the samples are qualified, and manufacturing pcb prototypes is expensive. To this end, FS Technology introduces the following methods for centralized testing of circuit boards:

How to detect the welding quality of FS PCB board

Visual inspection of pcb board

Manual detection is a widely used and long-standing method, and is still used by all PBC manufacturing companies even in today’s advanced technology. Visual inspection Use the human eye to observe the welding condition of the bare surface of the pcb board, in the early stage of manufacture, it is easy to detect welding defects (high dryness, improper material use, chassis falling off, bridging, small solder ball spatter, matte solder joints, missing solder etc.) The most used tool for manual inspection is a 5-10 times fixed magnifying glass. Such magnifying glass will not hurt the eyes of FS PCB employees, but also can clearly find welding defects, which is completely suitable for the inspection of low-density circuit board welding.

Of course, visual inspection of circuit boards also has certain defects, that is, it will make the inspectors tired. In order to solve this problem, FS Technology began to use more advanced visual inspection tools-camera screen display inspection instruments from 2019. It’s powerful. 1. Adjustable multiples, up to 80-90 times, can detect pcb welding defects more clearly; 2. Through CCD display on the screen, pcb inspectors can observe the circuit board like watching TV, which greatly reduces the fatigue of employees degree, increasing the detection accuracy. 3. More advanced detectors can automatically move the circuit board soldering in two directions, and can also automatically position to achieve the detection of key components of the PCBA. 4. Equipped with a video recorder, the test results can be recorded anytime and anywhere. After practical operation, this reduces the damage rate of circuit boards and assembled boards manufactured by FS Technology.

Infrared detection method for testing printed circuit boards

The infrared detection method refers to radiating heat from the infrared beam to the solder joints of the circuit board. Through the heat release curve reflected by the pcb solder joints, it is judged whether the pcba soldering is normal, so as to determine whether there are holes on the solder joints, and the most intuitive detection of the pcb Soldering quality during assembly. This method is widely used in the production of large-scale PCBs, with good pad consistency and small differences in component volume. Otherwise, other factors have too great influence on the heat dissipation characteristics of the solder joints. The false detection rate will increase. Generally, we seldom use it in electronic product testing, because due to the size and performance of different products, the feedback results will also be very different.

X-ray fluoroscopy to detect pcb

X-ray fluoroscopy is currently the most advanced and also the most expensive method. It exploits the fact that X-rays are not as capable of penetrating solder as copper, silicon, FR-4, and other materials, showing the density distribution of solder thickness, shape, and mass in pcb assembly. This method is used to detect concealed welding and small-area welding, more generally speaking, welding that is invisible to the human eye. The specific steps are very simple, that is, put the circuit board to be tested into the X-ray test channel, and you can clearly observe the solder joints of the circuit board through the display. FS Technology recommends that you must take precautions to prevent X-rays from passing through when using this detection method.

Advanced online testing methods

It can check open, shorted, and faulty components soldered to a circuit board, as well as component functionality such as resistance and capacitance values, transistor polarity, and more. Through the IC’s floating pin test method, it is possible to check the faulty solder pins of the IC.
The online test method is an electrical signal test method. It can detect the soldering state of circuit board soldering, which is very close to the actual situation.

A basic general purpose grating processor consists of a drill plate with 100, 75 or 50 mil center-to-center pins.  This completes the independent test. However, the proximity of the probes limits the performance of bed of needles testing.

Reliable and dense PCB inspection method

No matter how difficult the circuit is, FS Technology has a way to overcome it. In a sense, the detection that FS Technology PCBA company cannot do is basically impossible for other PCBA assembly companies in China. We can be said to be the company with the most advanced technology and the most comprehensive service items in China, not only providing pcb manufacturing, pcba, pcb testing, pcb components procurement services, we can also provide one-stop ems services for customers in need, the next is Specific methods to detect dense PCBs:

The most used method in FS is the bed of needles test

Flying probe testers do not depend on pin patterns mounted on a fixture or bracket. The two probes can move within 4 mils of each other. The probes can move independently, there is no practical limit to the distance between them. The tester with two movable arms is based on capacitance measurements.  If there is a short between the lines, the capacitance will be greater than a certain point. If there is an open circuit, the capacitance will decrease.

Test speed is an important criterion for selecting a tester. A bed of needles tester can accurately test thousands of test points at a time. While a flying probe tester can only test two or four test points on a circuit board at a time. Also, depending on the complexity of the board. A bed of needles tester may only take 20-30 seconds to perform a single-sided test. While a flying probe tester takes 1 hour or more to complete the same evaluation. Shipley &40;1991) explained that while high-volume PCB manufacturers consider mobile flying probe testing techniques to be slower. This method is a good option for low-volume and complex PCB manufacturers.

For bare board testing, there are special testing instruments. A more cost-optimized approach is to use a general-purpose instrument. For general purpose grids, the standard grid for lead components and surface mount devices is 2.5 mm. At this time, the test pad should be greater than or equal to 1.3mm.  The test pins are small, fragile and easily damaged. Therefore, it is better to use a grid larger than 2.5mm. The combination of a general-purpose tester (standard gate tester) . a flying probe tester can accurately and cost-effectively inspect high-density circuit boards. However, the height difference of the hot air leveling pads can hinder the connection of the test points.

microscope observation

In order to ensure that the PCBA board we produce can work normally. We use the most advanced observation instrument in the world to detect – a portable video microscope. With the portable video microscope. We can clearly observe the structure of the pcb and understand the distance between each plug-in and the motherboard. In addition, it can also provide favorable adjustments for us to design circuit boards. The portable video microscopes msa200 and vt101 currently used by FS Technology PCBA factory are more convenient and accurate than traditional microscopes.