Electronics are an integral part of our daily lives. Everything from our smart phones to our cars includes electronic components. At the heart of these electronics is the printed circuit board, also known as a PCB.
Most people recognize printed circuit boards when they see them. These are the small green chips covered in lines and copper parts you’ll find at the heart of gutted electronic devices. Made with fiberglass, copper lines and other metal parts, these boards are held together with epoxy and insulated with a solder mask. This solder mask is where that characteristic green color comes from.
However, have you ever observed those boards with components solidly stuck on? Never regard them as just decorations of a PCB board. An advanced circuit board won’t be able to give its functionality until components are mounted on it. A PCB with components mounted on is called an assembled PCB and the manufacturing process is called PCB assembly or PCBA for short. The copper lines on bare board, called traces, electrically link connectors and components to each other. They run signals between these features, allowing the circuit board to function in a specifically designed way. These functions range from the simple to the complex, and yet the size of PCBs can be smaller than a thumbnail.
So how exactly are these devices made? The PCB assembly process is a simple one, consisting of several automated and manual steps. With each step of the process, a board manufacturer has both manual and automated options from which to choose. To help you better understand the PCBA process from start to finish, we’ve explained each step in detail below.
The first step of PCB assembly is applying a solder paste to the board. This process is like screen-printing a shirt, except instead of a mask, a thin, stainless-steel stencil is placed over the PCB. This allows assemblers to apply solder paste only to certain parts of the would-be PCB. These parts are where components will sit in the finished PCB.Solder Paste Composition | PCBCart
The solder paste itself is a greyish substance consisting of tiny balls of metal, also known as solder. The composition of these tiny metal balls is 96.5% tin, 3% silver and 0.5% copper. The solder paste mixes solder with a flux, which is a chemical designed help the solder melt and bond to a surface. Solder paste appears as a grey paste and must be applied to the board at exactly the right places and in precisely the right amounts.
In a professional PCBA line, a mechanical fixture holds the PCB and solder stencil in place. An applicator then places solder paste on the intended areas in precise amounts. The machine then spreads the paste across the stencil, applying it evenly to every open area. After removing the stencil, the solder paste remains in the intended locations.
After applying the solder paste to the PCB board, the PCBA process moves on to the pick and place machine, a robotic device places surface mount components, or SMDs, on a prepared PCB. SMDs account for most non-connector components on PCBs today. These SMDs are then soldered on to the surface of the board in the next step of PCBA process.
Traditionally, this was a manual process done with a pair of tweezers, in which assemblers had to pick and place components by hand. These days, thankfully, this step is an automated process among PCB manufacturers. This shift occurred largely because machines tend to be more accurate and more consistent than humans. While humans can work quickly, fatigue and eyestrain tends to set in after a few hours working with such small components. Machines work around the clock without such fatigue.Surface Mount Technology | PCBCart
The device starts the pick and place process by picking up a PCB board with a vacuum grip and moving it to the pick and place station. The robot then orients the PCB at the station and begins applying the SMTs to the PCB surface. These components are placed on top of the soldering paste in preprogrammed locations.
Once the solder paste and surface mount components are all in place, they need to remain there. This means the solder paste needs to solidify, adhering components to the board. PCB assembly accomplishes this through a process called “reflow”.
After the pick and place process concludes, the PCB board is transferred to a conveyor belt. This conveyor belt moves through a large reflow oven, which is somewhat like a commercial pizza oven. This oven consists of a series of heaters which gradually heat the board to temperatures around 250 degrees Celsius, or 480 degrees Fahrenheit. This is hot enough to melt the solder in the solder paste.
Once the solder melts, the PCB continues to move through the oven. It passes through a series of cooler heaters, which allows the melted solder to cool and solidify in a controlled manner. This creates a permanent solder joint to connect the SMDs to the PCB.
Many PCBAs require special consideration during reflow, especially for two-sided PCB Assembly. Two-sided PCB assembly need stenciling and reflowing each side separately. First, the side with fewer and smaller parts is stenciled, placed and reflowed, followed by the other side.
Once the surface mount components are soldered in place after the reflow process, which doesn’t stand for completion of PCBA and the assembled board needs to be tested for functionality. Often, movement during the reflow process will result in poor connection quality or a complete lack of a connection. Shorts are also a common side effect of this movement, as misplaced components can sometimes connect portions of the circuit that should not connect.
Checking for these errors and misalignments can involve one of several different inspection methods. The most common inspection methods include:
• Manual Checks: Despite upcoming development trend of automated and smart manufacturing, manual checks are still relied on in PCB assembly process. For smaller batches, an in-person visual inspection by a designer is an effective method to ensure the quality of a PCB after the reflow process. However, this method becomes increasingly impractical and inaccurate as the number of inspected boards increases. Looking at such small components for more than an hour can lead to optical fatigue, resulting in less accurate inspections.
• Automatic Optical Inspection: Automatic optical inspection is a more appropriate inspection method for larger batches of PCBAs. An automatic optical inspection machine, also known as an AOI machine, uses a series of high-powered cameras to “see” PCBs. These cameras are arranged at different angles to view solder connections. Different quality solder connections reflect light in different ways, allowing the AOI to recognize a lower-quality solder. The AOI does this at a very high speed, allowing it to process a high quantity of PCBs in a relatively short time.
• X-ray Inspection: Yet another method of inspection involves x-rays. This is a less common inspection method — it’s used most often for more complex or layered PCBs. The X-ray allows a viewer to see through layers and visualize lower layers to identify any potentially hidden problems.
The fate of a malfunctioning board depends on PCBA company’s standards, they will be sent back to be cleared and reworked, or scrapped.
Whether an inspection finds one of these mistakes or not, the next step of the process is to test the part to make sure it does what it’s supposed to do. This involves testing the PCB connections for quality. Boards requiring programming or calibration require even more steps to test proper functionality.
Such inspections can occur regularly after the reflow process to identify any potential problems. These regular checks can ensure that errors are found and fixed as soon as possible, which helps both the manufacturer and the designer save time, labor and materials.
As a traditional PCB assembly method, thru-hole mounting process is accomplished through collaboration of manual procedure and automatic procedure.
• Step 1: Components Placement – This step is achieved manually by professional engineering staff. Engineers need to quickly, yet precisely place components on corresponding positions based on client’s PCB design files. Component placement must conform to regulations and operation standards of thru-hole mounting process to guarantee high quality end products. For example, they have to clarify polarity and orientation of components, to stop operating component from affecting ambient components, to make completed component placement compatible with corresponding standards and to wear anti-static wristbands when dealing with static-sensitive components like ICs.
• Step 2: Inspection & Rectification – Once component placement is completed, the board is then placed in a matching transport frame where board with components plugged in will be automatically inspected so as to determine whether components are accurately placed. If issues concerning component placement are observed, it’s easy to get them rectified immediately as well. After all, this takes place prior to soldering in PCBA process.
• Step 3: Wave Soldering – Now the THT components should be accurately soldered onto circuit board. In the wave soldering system, the board moves slowly over a wave of liquid solder at high temperature, approximately 500°F. Afterwards, all leads or wires connections can be successfully obtained so that thru-hole components are firmly attached to the board.
Compared with thru-hole mounting process, surface mounting process stands out in terms of manufacturing efficiency because it features a totally automatic mounting PCB assembly process from solder paste printing, pick and place and reflow soldering.
• Step 1: Solder Paste Printing – Solder paste is applied on the board through a solder paste printer. A template ensures that solder paste can be accurately left on correct places where components will be mounted, which is also called stencil or solder screen. Because quality of solder paste printing is directly associated with quality of soldering, PCBA manufacturers focusing on high quality products usually carry out inspections after solder paste printing through a solder paste inspector. This inspection guarantees printing has achieved regulations and standards. If defects are found on solder paste printing, printing has to be reworked or solder paste will be washed off prior to second printing.
• Step 2: Components Mounting – After coming out of solder paste printer, PCB will be auto-sent to pick-and-place machine where components or ICs will be mounted on corresponding pads in the effect of tension of solder paste. Components are mounted on PCB board through component reels in the machine. Similar to film reels, component reels carrying components rotate to provide parts to the machine, which will quickly stick parts to the board.
• Step 3: Reflow Soldering – After every component is placed, the board passes through a 23-foot-long furnace. A temperature of 500°F causes the solder paste to liquefy. Now the SMD components are bound firmly to the board.
Wave solderingis a kind of solder wave with a specific shape formed on the surface of molten liquid solder by means of pump pressure. When mounted components pass through the solder wave at a fixed angle, solder joints are formed in the lead solder zone. The component is preheated in the preheating zone of the welding machine (the preheating of the component and the temperature to be reached are still controlled by the predetermined temperature curve) in the process of conveyor belt conveyor. In actual welding, the preheating temperature of the assembly surface is usually controlled, so many devices have added corresponding temperature detection devices (such as infrared detectors). After preheating, the components enter the lead slot for welding. Tin trough contains molten liquid solder. The nozzle at the bottom of the trough determines the shape of the solder. Thus, the solder wave is heated when the welding surface of the component passes through the wave. At the same time, the solder wave wets the welding zone and expands and fills the welding process.
二、Basic working principle
Wave soldering is based on the principle of convection heat transfer to the welding area heating. The molten solder wave acts as a source of heat. On the one hand, it flows to wash out the pin welding area, on the other hand, it acts as a heat conduction. The pin welding area is heated under this effect. When the silver lead solder is used, the melting solder temperature is usually controlled at about 245 degrees Celsius. In order to ensure the temperature of the welding zone, the solder wave usually has a fixed width, so that when the welding surface of the component passes through the wave, there is sufficient time for heating and wetting. In traditional wave soldering, a wave is adopted and the wave is relatively flat. With the use of lead solder, double wave mode is adopted at present.
三、The welding spot
The pin of the component provides a way to immerse the liquid solder into the metal through hole. When the pin contacts the solder wave, the liquid solder climbs up along the pin and the hole wall with the help of the surface tension. The capillary action of metallized through-hole improves the climb of solder. When the solder reaches the PcB part, the surface tension of the pad is expanded. The rising solder discharges flux gas and air from the through hole, filling the through hole and forming a solder joint after cooling.
四、What’s the difference between wave soldering and reflow oven?
The mainly different are in heating source and solder supply mode. In wave soldering, the solder is pre-heated and melted in the trough. The solder wave pumped by the pump plays a dual role of heat source and solder supply. The solder wave of solder solder solder causes the through holes, pads and component pins of the PcB to be heated, and also provides the solder needed to form solder joints. In reflow soldering, solder paste is pre-quantitatively assigned to the solder zone of PCB. The role of heat source in reflow is to re-melt the solder.
五、Main components and working principle of wave soldering
A wave soldering machine is mainly composed of conveyor belt, heater, tin trough, pump, flux foaming (or spraying) device, etc. It is mainly divided into flux adding area, preheating zone and welding area.
The solder in the solder tank, heated by a heater, gradually melts, and the molten liquid solder, under the action of a mechanical pump (or electromagnetic pump), forms a specific shape of solder wave on the surface of the solder tank, which becomes a wave. The PCB with mounted elements is placed on the conveyor and solder joints are welded by passing through the solder wave at a certain angle and at a certain immersion depth, so it is called wave soldering.
For a single wave, there is only one wave, called the advection wave. For double waves, the first wave is called the disturbing wave, and the second wave is called the advection wave (Ping Huabo).
The role of spoiler: SMT element welding and prevent leakage welding, it ensures the proper distribution of solder through the circuit board. The solder is penetrated through the slit at a relatively high speed, thus leading to narrow gap. The direction of the jet is the same as that of the circuit board. For SMT components, the disturbance wave can basically be welded. But for through-hole components, the spoiler wave itself can not properly weld the components, it leaves the weld unevenness and excess solder, so the need for a second wave – advection wave.
The role of advection wave is to eliminate burr and weld bridge generated by the disturbance wave. Advection wave is actually the wave used by the single wave soldering machine. Therefore, when the traditional through-hole components are welded on the dual-wave machine, the disturbing wave can be turned off and the soldering can be completed by advection wave. The entire wavefront of the advection wave is basically horizontal, like a mirror. At first glance, it looks as if the tin wave is static, but in fact the solder is flowing continuously, but the wave is very smooth.
六、Wave soldering machine welding spot molding
Solder Joint Forming: When PCB enters the front end of the wave, the substrate and pin are heated, and before leaving the wave, the whole PCB is immersed in the solder, that is, bridged by the solder, but at the moment of leaving the wave end, a small amount of solder is attached to the pad due to the effect of wetting force, and due to surface tension, it will come out. At present, the shrinkage of the lead wire is small, and the wetting force between the solder and the pad is greater than the cohesion of the solder between the two pads. Therefore, a full, round solder joint will be formed, leaving the excess solder at the end of the wave, and due to gravity, it will fall back into the tin bath.
Bulk material handle method and process on SMT production line
SMT patch bulk material problems have plagued many SMT people, as we all know, once the placement machine starts, there will definitely be a problem in the SMT production line. For a variety of reasons, many bulk materials are produced, thrown, or are originally bulk materials, or other reasons. Some bulk materials, such as resistors, capacitors, inductors, etc., are not easily distinguishable and have little value in themselves, and there is no value for reuse. However, for large devices, especially some imported chip components, they are of high value and can be distinguished and distinguished, so they are generally reused. However, for scattered components, if the original package is a tray or a suitable tray, the problem may be solved better. Otherwise, it may be more difficult to handle. Southern Machinery today will talk about the handling of bulk material in the SMT production line. Method and process. First, the bulk material handle process
Collecting materials – material personnel sorting materials – using electrostatic bags to pack – paste material specifications – technicians based on bulk material springboard – hand paste bulk material – QC confirmation
Second, the definition
Bulk material: refers to the components that are separated from the original packaging during the production process due to machine throwing, or loading and unloading materials.
Third, job responsibilities
Material staff: responsible for the collection, classification, identification, storage, placement, and placement information of bulk materials, and the material loss rate is calculated according to the order.
QC in front of the furnace: responsible for the manual placement of bulk materials, the front back grain and material code confirmation, PCBA mark, and the classification of bulk materials.
Technician: Responsible for programming, patch production, monitoring patch quality distribution and timely improvement.
QC after the furnace: It is responsible for checking and checking the first piece of all the machines, and the quality is abnormal. Immediate feedback is provided to the front station to improve and track.
Fourth, the work content
In the production process, the material may be thrown due to equipment and other factors, so the operator should check the material step before the patch and after the shift, and check the throwing box and the trash can each time the garbage is dumped. Collect the bulk material and report to the supervisor about excessive bulk material anomalies.
According to the shape of the components, the bulk material is classified according to the shape of the components, and the back code of the components is checked to determine the material code. Then, the checked bulk materials are packed in anti-static bulk box or bulk bag, and the material code identification is performed to confirm the signature of the person. .
When using machine mounting, the operator should first check whether the components are consistent with the normal materials, confirm the material number, and then load the FEEDER tape.
The first piece of material feeding / mid-way refueling, the technician firstly inspects the materials that will be short of materials in the machine half-hour in advance, and collects the materials of the same item number in the component preparation area, and check them correctly, and submit them to the quality department QC/materials. The staff will check again and confirm the total signature of the refueling sheet.
The most important choice of laser marking machine is its laser.So today I’m gonna to tell you something about four most common lasers.
1. CO2 laser /（CO2 laser marking machine）
CO2 laser marking machine principle: CO2 laser marking machine, or carbon dioxide laser marking machine (CO2 is carbon dioxide). It is a laser galvanometer marking machine using CO2 gas as working medium. CO2 laser marking machine is a CO2 laser with CO2 gas as the medium, CO2 and other auxiliary gases are charged into the discharge tube on the electrode to add high voltage, the discharge tube produces glow discharge, so that the gas emits a wavelength of 10.64um laser, laser energy amplified, after the galvanometer scanning and F-Theta mirror focusing, under the control of computer and laser marking control card. The marking of images, words, numbers and lines can be carried out on the workpiece according to the requirements of users.
CO2 laser marking machine consists of CO2 laser, 10.64 field mirror, 10.64 beam expander, CO2 laser power supply, scanning galvanometer, control computer, laser control card, laser control software, laser frame, laser circulating water system, circuit control system and other parts.
3）Advantages and application areas
The main features of CO2 laser marking machine are: using carbon dioxide laser, belonging to the general model, post-focusing mode, small size, high integration.
This machine is suitable for marking most non-metallic materials, such as paper packaging, plastic products, label paper,leather cloth, glass and ceramics, resin and plastic, bamboo and wood products, PCB board, etc. CO2 laser is a gas laser with a wavelength of 10.64 um in the far infrared optical band. CO2 gas filled discharge tube is used as the medium to produce laser. When high voltage is applied to the electrode, glow discharge is produced in the discharge tube. The gas molecule can release the laser, and the laser beam is formed after amplifying the laser energy.
2.Green laser /（Green laser marking machine）
Green laser marking machine uses high-power multi-mode laser diode pumped to produce green laser beam after laser frequency doubling, and then through computer control of high-speed scanning galvanometer deflection marking or cutting. Two laser beams are projected from different angles into transparent objects (such as glass, crystal, etc.), accurately intersecting at a point. Because two laser beams interfere and cancel at the intersection point, their energy is converted from light energy to internal energy, releasing a lot of heat, melting the point into a tiny hole. The machine accurately controls the intersection of two laser beams at different locations, creating a large number of tiny holes that eventually form the desired pattern.
2）Advantages and application areas
The green laser with 532 nm wavelength has obvious advantages: smaller spot diameter, more concentrated energy, high electro-optic conversion efficiency, good beam quality, marking accuracy below 10 micron level, neat marking frame, no explosion point, no thermal deformation. Mainly used in glass, crystal products, surface and internal marking, ceramics, metals, electronics, plastics and other products. It belongs to the category of cold light. It is also suitable for some products with high heat reaction and high precision.
Through photochemical ablation, that is, by laser energy to break the bonding between atoms or molecules, making it into small molecules gasification, evaporation. The focus spot is very small and the heat affected zone is very small, so it can be used for superfine marking and special material marking.
The main components of UV laser marking machine are: focusing system, trigger type, computer control system, laser power supply, laser, galvanometer field mirror scanning system, marking control software.
3）Advantages and application areas
Ultraviolet laser marking machine with its unique low-power laser beam, especially suitable for ultra-fine processing of the high-end market.iPhone, cosmetics, pharmaceuticals, food and other polymer packaging bottle surface marking; flexible PCB board; silicon wafer micro-hole, blind hole processing; LCD liquid crystal glass, glassware surface, metal surface coating, plastic buttons, electronic components, Communications Equipment, and other fields.
Optical fiber laser marking machine principle: Optical fiber laser marking machine is the use of laser beams in a variety of different substances on the surface of permanent marking. Marking effect is through the evaporation of the surface material to expose the deep material, or through the light energy causes the chemical and physical changes of the surface material to “engrave” out the trace, or through the light energy burns off part of the material, showing the desired etched patterns, text, bar code and other graphics. The so-called fiber laser marking machine refers to the use of fiber laser marking machine, fiber laser with small size (no water-cooled device, using air-cooled), light is good quality (base mode), maintenance-free and so on.
Fiber laser marking machine is mainly composed of fiber laser, high-speed scanning mirror, marking software, industrial computer and cabinet. Fiber laser is the core part.
3）Advantages and application areas
Mainly used in: plastics, electronics, metals, ceramics, tobacco and other materials marked out the required text,pattern, bar code and other graphics. Optical fiber laser marking machine easy to operate, fast marking, clear and other advantages, making the production efficiency of enterprises more efficient. Our commonly used pulsed lasers are 10W, 20W, 30W and 50W.
We design and manufacture automatic machine for the PCB/SMT and Thru-hole industries in Shenzhen China. We help companies looking to low cost equipment with smart, ROI-driven assembly equipment solutions.Contact us today to learn how we can help you。
Dear ,After many requests, we are thrilled to announce our Industry Leader Newsletter. As an Industry Leader, Southern Machinery wants to provide your company with the same excellence we put into our equipment and services. We know your job is important and you must always stay ahead of trends in PCB Assembly. Changes in labor costs, shifting environmental laws and policies, energy conservation efforts, advancing industries, international trade politics, etc., are causing a reemergence of in-house manufacturing systems to be put into place. The tide has shifted and it is now time to begin transitioning to a more self-sufficient manufacturing system.
Welcome to our SMTHelp.com Newsletter! No matter what your company role is, this Newsletter will keep you up-to-date with the most important topics and events that affect the quality and profitability of your manufacturing systems. If it has been a while since we last spoke, stay tuned! We will be delivering important PCB topics to your inbox. In the meantime, we have put a quality checklist together for you!
Your Manufacturing Quality Checklist here:
Do you have ROI-Driven Design and Implementation of reliable PCB Assembly Equipment?
Is your equipment Low-Cost with High-Intelligence?
What is the speed of your PCB throughput?
Is your efficiency high?
Is your productivity high?
Are you increasing your profits by using affordable and reliable equipment?
Is your short-term investment low?
Is your long-term investment low?
Have you eliminated hand insertion for Automatic Insertion for improved time and profits?
Finally, have you eliminated your import fees by producing your own PCBs?