How to remove the misprinted solder paste on the PCB surface?
Prepared by Ming
ming@smthelp.com This article describes that paying attention to some details can often prevent common problems in assembly processes and equipment selection.
Question: Can I use a small spatula to remove misprinted solder paste from the board? Will this get the solder paste and small tin beads into the holes and small gaps?
Answer: Using a small spatula to remove the solder paste from the misprinted board may cause some problems. It is generally practicable to immerse the misprinted board in a compatible solvent, such as water with an additive, and then remove the small tin beads from the board with a soft brush. I prefer to soak and wash repeatedly instead of violent dry brush or shovel. After the solder paste is printed, the longer the operator waits to clean the misprint, the harder it is to remove the solder paste. Misprinted boards should be placed in the soaking solvent immediately after the problem is discovered, as the solder paste is easily removed before it is dried.
Avoid wiping with a strip of cloth to prevent solder paste and other contaminants from smearing on the surface of the board. After soaking, brushing with a gentle spray can often help remove unwanted tins. It is also recommended to dry with hot air. If a horizontal stencil cleaner is used, the side to be cleaned should face down to allow the solder paste to fall off the board.
As usual, note that some details can eliminate undesirable conditions, such as misprinting of the solder paste and removal of the solder paste from the board. It is our goal to deposit the right amount of solder paste at the desired location. Stained tools, dry solder paste, and misalignment of the stencils and plates can cause undesirable solder paste on the underside of the stencil or even the assembly. During the printing process, the template is wiped with a certain pattern between printing cycles. Ensure that the template is seated on the pad, not on the solder mask, to ensure a clean solder paste printing process. On-line, real-time solder paste inspection and inspection prior to reflow after component placement are process steps that reduce process defects prior to soldering.
For fine-pitch stencils, if damage is caused between pins due to thin stencil cross-section bending, it can cause solder paste to deposit between the pins, causing printing defects and/or short circuits. Low viscosity solder paste can also cause printing defects. For example, high operating temperatures or high blade speeds can reduce the stickiness of the solder paste during use, resulting in printing defects and bridging due to excessive solder paste deposition.
In general, the lack of adequate control of materials, solder paste deposition methods and equipment are the main causes of defects in the reflow soldering process.
Question: What type of assembly board depaneling equipment provides the best results?
Answer: There are several sub-board systems that offer a variety of techniques for slab assembly boards. As a rule, there are many factors that should be considered when selecting such a device. Regardless of whether there is routing, sawing or blanking to separate individual panels from the composite panel, stable support during the splitting process is the most important factor. Without support, the resulting stress can damage the substrate and solder joints. Distorting the plate, or stressing the assembly during the splitting, can result in hidden or significant defects. While sawing often provides minimal clearance, shearing or die cutting with tools can provide cleaner, more controlled results.
In order to avoid component damage, many assemblers attempt to maintain component solder joints at least 5.08 mm from the edge of the board when the splitter is required. Sensitive ceramic capacitors or diodes may require extra care and consideration.
1,Please visit : www.smthelp.com
2, Find us more: https://www.facebook.com/autoinsertion
Applications: IGBT packaging, LED eutectic, solder paste process, high clean soldering process, laser diode package, hybrid integrated circuit package, package cover package, MEMS and vacuum package.
Industry application: S-V series vacuum reflow soldering machine is an ideal choice for R&D, process research and development, high-capacity production, and is the best choice for high-end R&D and production in military enterprises, research institutes, universities, aerospace and other fields.The product weld void rate is as low as 3% or less.
Features:
It adopts imported heating parts, uniform temperature and high thermal compensation efficiency. It is suitable for CSP, BGA, automobile lamp, UV lamp, LED flip chip process, laser device package, IGBT power device package process soldering;
Special wind wheel design, large air exchange and stable wind speed;
Each temperature zone adopts forced independent circulation, independent PID control, and independent heating mode to make the furnace cavity temperature accurate and uniform, and the heat capacity is large: 4, the temperature rises quickly, from room temperature to working temperature ≦ 30 minutes;
Imported high-quality high-temperature high-speed motor has stable wind, low vibration and low noise;
The furnace body adopts double cylinder (electric push rod) jacking device, which is safe and reliable; 7, chain, mesh belt synchronous constant speed transportation, using frequency conversion precision high speed; 8, special high-quality aluminum alloy rail design, small deformation, chain automatic refueling device; 9, UPS power-off protection function, to ensure the normal output of the PCB after power-off, not damaged;
Powerful software function, monitor and measure the temperature of the PCB board online, and analyze, store and print the data curve at any time;
11, industrial control PC and PLC communication using MODBUS protocol, work stable, to prevent the phenomenon of crash;
12, automatic monitoring, display equipment working status, you can make correction parameters at any time;
Special patented furnace design, good thermal insulation, and the lowest power consumption in the same industry;
The patented guide rail is not deformed at high temperature, and the three-wire rod synchronously widens the structure, effectively ensuring that the guide rails are parallel, preventing the board from falling, the occurrence of the card board, no cleaning, and easy adjustment. The adjustment operation can be performed both automatically and manually.
Standard chain and net chain synchronous iso-speed parallel transportation, can process single-sided and double-sided PCB boards, and optional double-rail transportation system.
The automatic width adjustment system adopts closed-loop PID control, which can be automatically adjusted to the required width according to the parameters input by the computer, and the accuracy can reach 0.2mm.
Due to the modular design of each temperature zone, hot air motor and heating wire are convenient for maintenance and repair.
18, strong cooling air cooling, cold air exchange fast, uniform wind speed, slope can be controlled by frequency conversion, tin point is smooth and bright;
The nitrogen flow meter can monitor the nitrogen flow at any time;
20, in the traditional SMT welding process, to improve, reduce the voids in the solder, the void rate can reach less than 5%;
21, high-quality products for mass production, the shortest product welding process cycle is 30S, to maintain continuous production;
At the same time, the equipment meets the traditional SMT process production configuration, nitrogen welding process and air welding process;
The vacuum part is independently controlled, and can be configured according to the process of the product, or can be shielded with the traditional process product to close this function;
Model
S-V8000
Heating part parameters
Number of pre-zones
8/8
Heating zone length
3000mm
number of cooling zones
2/2
Vacuum zone
Number of vacuum zones
1
Product size
smallest size:100*100MM；biggest size:300*350MM，
vacuum
10-100pa
Vacuum pumping speed
40m³/h Adjustable
Visual observation window
1
Heating system (optional)
Space maximum temperature 350 degrees
Flux recovery system
Reduces equipment maintenance and increases component life
System Control
Touch Screen + Siemens PLC
Process control action
Vacuuming time, vacuum pressure, vacuum pumping speed, vacuum maintenance time, deflation time free control setting
Transmission part parameters
Mesh belt width
500MM
Transport rail adjustment range
50-450MM
Transmission direction
L-R(R-L)
Transportation height
900±20MM
Transmission mode
mesh belt + chain transmission
Transmission speed
300-2000mm/min
power supply
Three five-line 380V 50/60HZ
Starting power
52KW
Normal work consumption Approx
Approx.10KW
Heating time
20min
Temperature control range
Room temperature -350 degrees
Temperature control
Full computer PID closed loop control, SSR drive
Machine control mode
PC+PLC
Temperature control accuracy
±1
PCB board temperature distribution difference
±1-2
Cooling method
Cold water cooling
Alarm temperature
Abnormal temperature (super high temperature or ultra low temperature after constant temperature)
Tricolor light indication
Three-color signal indicator: yellow – warming green – constant temperature red – abnormal
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.
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.
As we know,reflow oven is the most important welding technology in surface mount technology. It has been widely used in many industries including mobile phones, computers, automotive electronics, control circuits, communications, LED lighting and many other industries. More and more electronic devices are converted from through hole to surface mount, and reflow oven replaces wave soldering is a obvious trend in welding industry.
So what is the role of reflow oven equipment in the increasingly mature lead-free SMT process? Let’s take a look at the whole SMT surface mount line:
The whole SMT surface mounting line consists of three parts, such as steel mesh solder paste printing machine, SMT machine and reflow oven furnace. For the machine, and compared with lead free, and no new demands on the equipment itself; for screen printing machine, and a lead-free solder paste in the physical properties there are some differences, so put forward some improvement on the device itself, but there is no qualitative change. the key of lead-free is in the reflow oven.
The lead paste (Sn63Pb37) melting point of 183 degrees, if you want to form a good weld must have the thickness of 0.5-3.5um intermetallic compounds in welding, intermetallic compound formation temperature is above the melting point of 10-15, the lead welding is 195-200. The maximum withstand temperature of the electronic device on the circuit board is generally 240 degrees. Therefore, for lead welding, the ideal welding process window is 195-240 degrees.
Because of the change of melting point of lead-free solder paste, lead-free welding has brought great changes for welding process. At present, the lead-free solder paste is Sn96Ag0.5Cu3.5 and the melting point is 217-221 degrees. Good lead-free solder must also be formed 0.5-3.5um thickness intermetallic compounds, intermetallic compound formation temperature is also above the melting point of 10-15 degrees, for lead-free welding, that is, 230-235 degrees. Since the highest temperature of lead-free solder electronic device will not change, therefore, for lead-free soldering, ideal welding process window is 230-245 degrees.
The substantial reduction of process window brings great challenge to ensure welding quality, and also brings higher requirements to stability and reliability of lead-free wave soldering equipment. Because the equipment itself is coupled with the electronic device transverse temperature difference, due to differences in size of heat capacity will produce temperature difference in the heating process, so in the process control of lead-free reflow oven can be adjusted in the process of welding temperature window becomes very small, this is the real lead-free reflow to the difficulty.
High mixed, high value, low volume business expertise service.
Flexible operation, fast response and total satisfaction.
Good after-sales and extra value creation services including logistics support, valet procurement, supplier audit service and in factory office offering.
How to print soldering flux on the bottom pad of BGA
In general, Use flux soldering of high viscosity, to splice and process, should ensure that the printing pattern is clear, the overflow flux.
Sometimes,solder paste can be replaced by solder paste, and the metal component of solder paste should be matched with the metal component of solder ball.
When printing, BGA special small template is used. The thickness and opening size of the template should be determined according to the ball diameter and the ball distance.
After printing, the printing quality must be checked. If it is unqualified, it must be printed again after cleaning.
The latest introduction of PCB loader/unloader 2017
Characteristics of the equipment.
1.Special aluminum alloy mechanism to better understand the operation status of magazines.
Stable casting platform structure design, improve the stability of equipment 0.3. Panasonic PLC control, multi-function circuit and program design, performance stability, ensure the smooth and smooth production line.
Humanized programming, 4 kinds of PITCH selection, can set the step distance of receiving/transmitting PCB.
Standard SMEMA communication interface, which can communicate with other automation equipment.
The material box shall be transported by the engineering plate.
Adjustable push plate speed control.
Three-point positioning type upper and lower pneumatic clamping, ensure the location of the material box is accurate.
Push plate protection system to ensure that PCB board is not crushed, reducing process loss. This equipment adopts SMT circuit board production line operation
PCB size: (mm)： 50 x50~330 x445
Working height (mm)： 900 + 20 (STD)
groove Change time: bout 6 seconds
The machine size ：1650(L)845（W）1250（H）
Step selection: 10.20.30.40 mm
Power supply: AC 110/220v plus or minus 10V, 50/60hz knife bank
Dimensions (L * W * H, MM) : 355 (L) * 320 (W) * 565 (H)
Air pressure and gas flow : 4-6bar / 10 litres/min
Weight (KG)：140 kg
loader
This equipment is used SMT circuit board production line operating upper and lower plates
PCB SIZE:（mm）:50×50~330×250
Working height (mm):900±20(std)
Tank replacement time: about 6 seconds
Machine dimensions:1920(L)845（W）1250（H）
Step Select: 10.20.30.40 mm
Power Supply: AC 110/220V±10V, 50/60HZ
Magazine size (LWH，MM):355（L)320(W)565(H)
Barometric pressure and gas flow rate: ４－６bar/up to 10 l / min
Weight (KG):260KG
PCB Automatic UNloader
This equipment is used SMT circuit board production line operating upper and lower platesAI smt line
If you want to get more product introductions, please contact us: www.smthelp.com
ming@smthelp.com
jasonwu@smthelp.com
