What is PCBA?

PCBA is the whole manufacturing process of assembling various electronic components on the circuit board through surface packaging process. Which is the process of doing SMT or THT plug-in to the bare PCB bare boards.

SMT is a surface assembly technology , which is the most popular technology and process in the electronic assembly industry. Electronic circuit surface mount technology  is called surface mount or surface install technology. It is a circuit assembly technology that installs the surface assembly components without pins or short leads (SMC / SMD, i.e. chip element) on the surface of printed circuit board  or other substrate, and then solder them by reflow soldering or immersion soldering.

THT is a through-hole technology, which is, insert the electronic components into the reserved through-hole on the PCB, temporarily fix them and weld them on the other side of the substrate to form reliable solder joints and establish long-term machine and electrical connections. It is mainly applicable to electronic components with plug-ins when the size is large and is not suitable for patch or when the manufacturer's production process cannot use SMT technology. At present, there are mainly two methods: manual plug-in and machine plug-in.

Basic production process

There are two basic processes for PCBA production: one is SMT: reflow soldering; The other is THT: wave soldering

1. SMT: reflow soldering

Definition: reflow soldering refers to a soft soldering process to realize the mechanical and electrical connection between the solder end or pin of surface mount components and PCB pad by melting the solder paste pre-printed on PCB pad. It mainly depends on the effect of hot air flow on the solder joint. The colloidal flux reacts physically under a certain high-temperature air flow to achieve SMD soldering.

Process features: (1) the application and heating of solderare carried out separately, and the size of solder joint is controllable;

(2) The solder paste is distributed by printing. Generally, only one stencil is used for solder paste printing on each soldering surface:

(3) The main function of reflow furnace is to heat the solder paste. It is to heat the PCBA placed in the furnace as a whole. When soldering the second side, the welded joint on the first side will melt again.

Process flow: printing solder paste - SMT - reflow soldering - Cleaning - Inspection

2. THT: wave soldering

Definition: wave soldering refers to a soft soldering process in which the molten soft soldering solder is sprayed into a solder wave peak through a mechanical pump or electromagnetic pump, so that the PCB with pre-installed components passes through the solder wave peak to realize the mechanical and electrical connection between the component soldering end or pin and the PCB socket / pad.

Process features: (1) Apply solder and heat to PCB.

(2) heat is applied mainly through molten solder, and the amount of heat applied to PCB mainly depends on the temperature of molten solder and the contact time between molten solder and PCB soldering time.

(3) the size and filling of solder joint mainly depend on the design of pad and the installation gap between hole and lead. That is, the size of wave soldering joint mainly depends on the design.

(4) When soldering SMD, there is a "shielding effect", which is prone to missing soldering. The so-called " shielding effect " refers to the phenomenon that the package of chip SMD prevents the solder wave from contacting the solder end of the pad.

Process flow: dispensing - patch - curing - turnover - wave soldering - Cleaning - Inspection

(drawing with wave soldering) (drawing of wave soldering furnace)

If the two processes are mixed or reused, they can evolve into a variety of processes.

The complete PCB Assembly production process

PCBA usually includes through-hole plug-in components (THC / THD) and surface mount components (SMC / SMD). Only a small part of all surface mount components are used. Typical PCBA assembly processes include: full surface assembly, single-sided mixed assembly and double-sided mixed assembly.

The following describes the most common surface assembly method: mixed loading on one side, and SMC / SMD and THC / THD are all on side a. the production process of each company will be different. Take the production process of AiPCBA as an example.

1. Preparation before production

(1)Preparation of production documents: prepare relevant PCB fabrication files to guide production. The PCB fabrication files must be accurate. The accuracy of PCB fabrication files comes from the accuracy of design. In practice, many revisions will be made from product sample production to final mass production. In view of this problem, AiPCBA will solve the problem in the R & D stage. Our Solution is using our online PCBA simulation Manufacturing Verification Platform – AiEMA. The core function of AiEMA is to provide the function of PCB manufacturing and SMT mounting DFM analysis, avoid various risks for product design and manufacturing, provide the best solution, and strictly keep all customers files confidential.

(2) Material preparation: Preparing material, Receiving material, Counting material, material return and material storage.

Preparing material: materials are purchased according to the BOM documents. AiPCBA has experienced purchasing team to purchase raw materials, and all incoming materials are original.

Receiving material: inspect purchased materials. AiPCBA conducts sampling inspection for large batches and full inspection for small batches.

Counting material: count the quantity and model of materials according to the BOM file;

Material return: return materials with wrong model;

Material storage: store the tested materials in a specific environment. Electronic components must be stored at a constant temperature when stored in the incubator. Electronic components that need dehumidification or have temperature requirements are stored in the baking area. AiPCBA has a smart warehouse to store them according to the storage conditions of electronic components, so as to ensure that the inherent reliability of electronic components is not affected It can be automatically transmitted to the production line during production, which greatly improves the production efficiency.

(3) PCB bare board detection: clean and bake the PCB that has been unpacked, the length of time of root opening and whether it is affected by moisture and pollution.

(4) Evaluation process: it is mainly to order stencil and fixtures. In order to reduce the time and cost of outsourcing from other factories, AiPCBA's stencil is opened by itself, made in strict accordance with the production process documents and automatically transmitted to the production line. AiPCBA can accurately weld materials without making fixtures and using selective soldering machines without fixtures.

(5) Programming: engineers prepare the program in advance and then import it into the equipment. AiPCBA has professional engineers to program, and set some test points on the PCB in advance to test the continuity of PCBA circuit after PCB soldering all parts, so as to improve the reliability of products.

(6) Select the feeder: select the appropriate feeder according to the specification and type of electronic components, and correctly install the tape feeder of electronic components.

(7) Check equipments: check the power supply of the mounter, the vacuum and air pressure of the mounter, and install PCB positioning device, etc.

2. Formal production process

(1) For material picking, relevant personnel shall go to the smart warehouse to pick up some good materials according to the BOM file.

(2) SMT loading is to load the materials onto Feeder, and the details can not be ignored. Carefully read whether the material description is consistent with the material tray, take one from Feeder loaded with materials, keep the bottom, record the refueling time, take out Feeder in time, and take out Feeder in time when the material tray is used up.

(3) Install the stencil, which is a special template for SMT. It is mainly made according to the production documents of PCB. Its main function is to help the deposition of solder paste, so as to transfer the accurate amount of solder paste to the accurate position on the bare PCB.

(4)Printing Solder paste, PCB solder paste printing is mainly completed by the automatic printer, which is located at the front end of the SMT production line and is used to print solder paste or paste film. After the mesh of the stencil is aligned with the PCB pad, the solder paste or patch glue placed on the stencil is leaked to the corresponding position of the PCB pad through the movement of the scraper, so as to prepare for the installation of electronic components. AiPCBA uses SPI Sinic -Tek equipment to detect the solder paste, whose model is S8080, which can conduct 100% three-dimensional detection of the solder paste. In order to ensure the performance of the solder paste, AiPCBA has been stored it in cold storage and opened after warming.

(5)SMT process is mainly completed by the automatic mounter machine, also known as the placement machine, which is located behind the printing machine or dispensing machine. It is mainly to accurately take out the specified materials from the specified position and correctly install them to the specified position through preset conditions. AiPCBA's mounter machine is the most technologically advanced, complex and expensive equipment in the production line, which can paste hundreds of pieces at the same time Materials on the machine, avoid manual errors, automatically identify material code information, reduce material dislocation, accurate and meticulous patch, and the minimum mounted component is 01005.

(6) Pre-furnace mounting inspection: pre-furnace inspection is the inspection before reflow / wave soldering, mainly to check whether the patches are reversed, misaligned, multiple pieces, etc. AiPCBA uses AOI Holly equipment for testing, the model is lx520il, which can detect 100% of the machine mounting.

(7) During reflow soldering, the most important thing is to set the reflow soldering temperature curve. AiPCBA engineers set the temperature curve according to the physical and chemical changes of the solder paste during reflow soldering, which reduces the unhealthy soldering and further improves the quality and efficiency of production.

(8) AOI detection, AOI is a device based on optical principle to detect common defects encountered in soldering production, and automatically detect various mounting errors and soldering defects.

(9)X-ray detection is to detect the position where the sample cannot be detected by appearance. The change of light intensity after X-ray penetrates substances with different densities can form an image to show the internal structure of the object to be tested, and then observe the problem area inside the object to be tested without damaging the object to be tested. AiPCBA uses X-ray Ge equipment for detection, model PHoenix Xiaminer can perform 3D omni-directional detection and carry CT function.

(10) After furnace’s solder inspection, After furnace’s inspection is the inspection after reflow / wave soldering, mainly to check whether there are false soldering, offset, multiple pieces, less tin and other defects after curing. AiPCBA uses AOI Holly equipment for inspection, model lx520d, which can detect 100% of machine solder.

(11)First article inspection: it refers to the inspection of the first pcs. The main purpose of the first article inspection before the series production is to find the loopholes and deficiencies in product quality management and process management, so as to achieve better improvement. AiPCBA adopts the intelligent first article inspection equipment-Bluiris,which can intelligently prevent errors and control risks.

(12) AI automatic plug-in process mainly uses automatic plug-in equipment to insert electronic components into the conductive through hole of printed circuit board.

(13) Manual plug-in is to manually plug in electronic components that are inconvenient for machines.

(14) The most important thing in wave soldering is setting the wave soldering temperature curve. AiPCBA’s engineers set the temperature curve according to the physical and chemical changes of solder paste during solder reflow soldering.

(15) Trimming & splitting. Trimming is to cut off the excess length of pins of electronic components welded on the PCB, so as to meet the IPC standard and not easy to cause short circuit. Splitting is generally for panels, that is, to separate multiple PCBA panels.

(16) Solder joint repair, that is, holding tin, manual soldering for continuous soldering, no soldering, false soldering, etc.

(17) Appearance inspection is mainly to check the solderability, PCB / part damage, etc.

(18) Board Surface cleaning, that is, board cleaning, mainly to clean the adhesive large amount of rosin and other flux residues when cleaning solder, so as to make the circuit board look much cleaner and prevent corrosion of the circuit board.

(19) ICT detection is a standard test method to check the production and manufacturing defects and poor components by testing the electrical performance and electrical connection of online components. It mainly checks the online component faults, soldering faults, open and short circuit of each circuit network. It has the characteristics of simple operation, fast and accurate fault location.

(20) FCT intermediate test refers specifically to the function test of PCBA. When the product is powered on, test the parameters of the product when it works normally.

(21) PCBA assembly inspection is mainly to check some obvious problems in PCBA assembly.

(22) load aging test: conduct comprehensive aging test in advance to eliminate product faults.

(23) FCT final test: after load aging, conduct FCT test again to test the product function.

(24) Put on product labels to prevent confusion.

(25) final appearance inspection: conduct the last inspection on the appearance of PCBA.

(26) packaging, the most basic thing is to protect goods, and it can also be convenient for storage, transmission, etc.

(27) QA inspection, including confirmation of product quantity, product verification, product inspection, etc.

(28) finished qualified products shall be put into warehouse.

The figure below shows several typical PCBA assembly methods:

How to ensure the quality of PCBA?

The PCBA manufacturing process is complicated, involving a series of processes such as PCB board manufacturing, PCBA incoming component procurement and inspection, SMT processing, THT plug-in processing, post soldering processing, program burning, PCBA testing, aging, etc. the standardized operation in any link will seriously affect the quality of PCBA. Therefore, the whole PCBA processing process is very important. Mainly the following 7 aspects:

1. PCB board manufacturing

It mainly carries out process analysis for PCB drawings and documents, and submits manufacturability report (DFM) according to different customer needs, so as to avoid quality problems caused by poor PCB design and prevent a lot of rework and repair work.

2. Procurement and inspection of PCBA incoming components

The procurement, inspection and preservation of electronic components is a crucial link in PCBA production. It is necessary to strictly control the procurement channels of electronic components. AiPCBA provides one-stop PCBA services, from procurement,prototype, small batch production to mass production. The BOM purchasing efficiency of AiPCBA is the first in the whole network. All incoming materials are original channels or the original factory, and we help compare prices from different original source. Our alternative selection scheme can maximize the time and cost of purchasing electronic components.

3. SMT patch

It mainly involves stencil production, solder paste printing and temperature curve setting of reflow soldering furnace. Solder paste must be well controlled in this process.

4. THT plug-in processing

Traditionally, the mould design should be carried out before wave soldering. The application of mould carrier can significantly improved plug-in process, but in some cases,also do not need to make mould.

5. Program burning

Ensure that the program is written by professional engineers, and set some test points on the PCB in advance to test the continuity of PCBA circuit after PCB soldering all parts, so as to improve the reliability of the product.

6. PCBA board test

The main test contents include ICT (circuit test), FCT (function test), aging test, temperature and humidity test, drop test, etc. each process must be strictly tested by professionals to maximize the quality of products.

7. Advanced equipment

Advanced production equipment and testing equipment can strictly control the quality level of PCB circuit and improve efficiency while ensuring product quality.