Circuit board PCBA processing process is introduced

Circuit board PCBA processing process can be roughly divided into: empty board loading -> Printing solder paste -> Mount device -> Reflow welding -> AOI test -> Receiving plate -> Finished item inspection -> Parts after welding -> Circuit board open/short circuit test -> Circuit board function -> Test the cutting plate.

PCBA circuit board processing process

1. Load the empty plate

The first step of the assembly of the circuit board is to arrange the empty boards neatly, and then put them on the material rack. The machine will automatically send the boards into the SMT production line one by one.

2. Print solder paste

The first step for the PCB to enter the SMT production line is to print solder paste, which is a bit like applying a mask on the face of a girl. Here, the solder paste is printed on the welding pad of PCB parts that need to be welded, and the solder paste will melt and weld the electronic parts on the board after going through the high-temperature back welding furnace.

In addition, some people will use adhesive film board/adhesive paper board instead of solder paste when testing new products, which can increase the efficiency and waste of SMT adjusting machine.

3. Solder Paste Inspection machine

Because the solder paste printing is related to the welding quality of the following parts, some SMT factories will use optical instruments to check the solder paste printing quality after the solder paste printing. If there is a bad printing board, the solder paste will be knocked off, the solder paste will be washed off and reprinted, or the excess solder paste will be removed by repairing.

4. Fast printing machine

Here, some small electronic parts (such as small resistance, capacitance, inductance) will be hit on the circuit board. These parts will be slightly stuck by the tin paste just printed on the circuit board. So even if the speed of the printing is very fast, almost like a machine gun, the parts on the board will not fly away, but the large parts are not suitable for use in the fast machine. One will drag the speed of the small parts that were originally played very fast, and the other is afraid that the parts will offset the original position because the board moves quickly.

5. Universal type printing machine

Also known as "slow machine", here will be a number of large volume of electronic parts, such as BGA IC, connector... Etc., these parts need to be more accurate position, so the alignment is very important. Before typing, the camera will first take a look to confirm the position of the parts, so the speed is much slower. Because of the size of the parts here, they may not always have coil packaging, some may be tray or tubular packaging. However, an additional machine is required to enable SMT machines to eat pallets or tubes of packaging material.

Generally, the traditional printing/attaching machine uses the principle of suction to move electronic parts, so the top of these electronic parts must have a plane for the suction nozzle of the printing machine to absorb parts, but some electronic parts are unable to have a plane for these machines, at this time, it is necessary to tailor special suction nozzle for these special-shaped parts. Or add a layer of flat tape to the parts, or wear a flat cap.

6. Hand swing parts or visual inspection

When all the parts are wired to the circuit board before going through the high-temperature back welding furnace, a checkpoint is usually set up to pick out the offset or missing parts... And so on the shortcomings, because after the high temperature furnace if there is still a problem must be moved to the iron, it will affect the quality of the product, there will be additional costs; Other large electronic parts or traditional DIP/THD parts or parts that for some special reason cannot be operated by the printing/attaching machine will also be manually swung here.

In addition, an AOI will be designed for SMT of some mobile phone plates in front of the back welding furnace to confirm the quality before the back welding. Sometimes, the shielding frame will be placed on the parts, which will make it impossible to use AOI to check the solderability after the back welding furnace.

7. Back weld

The purpose of backwelding is to melt the solder paste and form nonmetallic copides in the parts foot and circuit board, that is, to weld electronic parts on the circuit board, the curve of temperature rise and fall often affects the quality of the entire circuit board welding, according to the characteristics of solder, the general backwelding furnace will be set preheating area, infiltration area, back welding area, cooling area to achieve the best soldering effect.

At present, the melting point of SAC305 solder paste without lead process is about 217℃, that is to say, the temperature of the backwelding furnace must be higher than this temperature at least in order to re-melt the solder paste. In addition, the highest temperature in the backwelding furnace should not exceed 250℃, otherwise many parts will be deformed or melted because they cannot withstand such a high temperature.

Basically, after the circuit board through the welding furnace, the assembly of the entire circuit board is completed, if there are hand welding parts exception, the rest is to check and test the circuit board has no defects or poor function.

8. Optical check for solderability

Not every SMT production line has an optical inspection machine (AOI). The purpose of AOI is to replace some circuit boards that are too dense for subsequent on-off and short-circuit electronic testing (ICT). However, AOI has its blind spots for optical interpretation, for example, the solder under parts cannot be judged. Currently, we can only check the parts for tombstone or side stand, missing parts, displacement, polarity direction, tin bridge and air welding, but we cannot judge the parts quality such as false welding, BGA weldability, resistance value, capacitance value and inductance value. So far, we cannot completely replace ICT.

Therefore, if only AOI is used to replace ICT, there is still some risk in quality, but ICT is not 100%. It can only be said that the test coverage rate can compensate each other, and we hope to achieve 100%, so we have to make a choice.

9. Retract the board

Once assembled, the boards are retracted to the racks, which have been designed to allow the SMT machine to automatically remove and remove the boards without compromising their quality.

10. Finished item inspection

No matter whether there is an AOI station or not, the general SMT line will still set up a visual inspection area for the circuit board. The purpose is to check whether there is any defect after the assembly of the circuit board. If there is an AOI station, the number of visual inspection personnel can be reduced, because it is still necessary to check some places where AOI cannot be interpreted, or check the defects of AOI.

Many factories will provide visual inspection templates at this station to facilitate visual inspection personnel to check some key parts and parts polarity.

11. Parts after welding

If there are parts that cannot be printed with SMT, a touch-up (post-process repair) hand welding of the part is required, which is usually placed after the finished product inspection to distinguish whether the defect is from SMT or later process.

After welding parts to use the soldering iron and tin wire, welding will be maintained at a certain high temperature of the soldering iron contact with the foot of the part to solder, until the temperature rises enough to melt the tin wire, and then add the tin wire melting, tin wire cooling will weld the parts on the circuit board.

When welding parts by hand, there will be some smoke, which will contain many heavy metals, so the operation area must be set up smoke discharge equipment, and try not to let the operator inhale these harmful fumes.

Need to remind, some parts will be due to the needs of the process and arranged in the later section of the process.

12. Circuit board open/short circuit test

The purpose of ICT setup is mainly to Test whether the parts and circuits on the Circuit board are open and short circuited. In addition, it can also measure the basic characteristics of most parts, such as resistance, capacitance and inductance values. To judge whether these parts after high temperature back welding furnace function damage, wrong parts, missing parts... Etc.

Circuit testing machines are divided into advanced and primary testing machines. The primary testing machine is commonly referred to as MDA(Manufacturing Defect Analyzer), whose function is to measure the basic characteristics of electronic parts mentioned above and determine the opening and short circuit.

In addition to containing all the functions of the first level of the Test machine, the advanced test machine can also be powered to the board under test, and the board under test can be started and the test program can be executed. The advantage is that the functional test of the circuit board can be simulated when the circuit board is actually started up and can partially replace the later Function test machine (Function Test). But a test fixture of this high level test machine can probably buy a private car, compared with a test fixture of the first level is 15~25 times higher, so it is generally used in the mass production of products.

13. Circuit board function test

Functional testing is to make up for the deficiency of ICT, because ICT only tests the on-off short circuit on the circuit board, and other functions such as BGA and products have not been tested, so it is necessary to use a functional testing machine to test all functions on the circuit board.

14. assembly board de-panel

General circuit boards will be assembled to increase the efficiency of SMT production, usually there will be so-called "several in one" board, such as two in one, four in one... Etc. Once all the assembly work is done, the board is cut into a single board, and some boards with only one board need to be cut off some of the excess edges.

There are several methods for cutting circuit boards, such as V-cut and using blade cutting machine or manual plate breaking (not recommended). For precise circuit boards, a path split-cutting machine/Router is used, which does not damage electronic parts and circuit boards, but costs and working hours are longer.

Shenzhen kingford PCBA processing factory

Shenzhen kingfordPCBA processing advantages

1. Strength guarantee

▪SMT workshop: We have imported SMT machines and several sets of optical inspection equipment, with a daily output of 4 million. Each process is equipped with QC personnel, who can keep an eye on product quality.

▪DIP production line: We have two wave-soldering machines, among which there are more than 10 old employees who have worked for more than three years. The skilled workers can weld all kinds of plug-in materials.

2. Quality assurance, cost-effective

▪ High-end equipment can stick precision shaped parts, BGA, QFN, 0201 materials. Can also template patch, loose material hand.

▪ Sample and size batch can be produced, proofing from 800 yuan, batch 0.008 yuan/point, no start-up fee.

3. Rich experience in SMT and welding of electronic products, stable delivery

▪ Accumulated SMT SMT processing services for thousands of electronic enterprises, involving many kinds of automotive equipment and industrial control motherboard. The products are often exported to Europe and the United States, and the quality can be affirmed by new and old customers.

▪ On time delivery, normal 3-5 days after complete materials, small batch can also be expedited on the same day shipment.

4. Strong maintenance ability and perfect after-sales service

▪ Experienced maintenance engineers can repair all kinds of patch welding caused by bad products, to ensure the connection rate of each piece of circuit board.

▪ 24-hour customer service staff at any time response, the fastest speed to solve your order problems.