01 ABC Sharing Session - Product Processing Operations
a. Solder Paste Printing
This process requires a stencil, also known as a steel mesh. The stencil is designed with openings corresponding to the PCB pads, and its thickness determines the solder paste thickness. Since the quality of solder paste printing directly affects subsequent soldering quality, parameters such as squeegee speed and pressure must be carefully adjusted before printing.
The required tooling for solder paste printing is the stencil, which is custom-made based on the PCB design. The price varies depending on the process, typically ranging from 300 to 1,000 RMB per stencil. The consumable used in solder paste printing is solder paste, which can be categorized as leaded or lead-free. Due to increasingly stringent environmental requirements, lead-free solder paste is more commonly used today, though it is slightly more expensive than leaded solder paste. Different types of solder paste should not be mixed, and solder paste must be returned to room temperature and stirred before use.
b. Pick and Place (P&P)
Also known as SMT (Surface Mount Technology). P&P requires specialized placement programs, a universal feeding system, and nozzles that are generally universal, though some irregularly shaped components may require custom systems developed by the manufacturer.
Types of Placement Machines by Function:
High-Speed Machines: Primarily handle regular-sized surface-mount components such as resistors and capacitors.
Typically equipped with 10–15 work heads, each capable of holding 2–5 nozzles.
Placement speed: 10+ components per second.
Each SMT line usually includes 1–3 high-speed machines.
High-speed machines may experience material wastage, so sample-stage material preparation should include a 10% buffer rather than relying on exact quantities.
Universal Machines: Capable of placing large and irregularly shaped components.
Typically equipped with 3–5 work heads, each capable of holding 2–5 nozzles.
Placement speed: 1–2 seconds per tape-fed component, 1–3 seconds per tray-fed component.
Each SMT production line typically includes one universal machine.
Types of Placement Machines by Speed:
Medium- to Low-Speed Placement Machines: Theoretical placement speed below 30,000 components per hour (for chip components).
High-Speed Placement Machines: Theoretical placement speed between 30,000 and 60,000 components per hour.
Ultra-High-Speed Placement Machines: Theoretical placement speed above 60,000 components per hour.
c. Component Soldering - Reflow Soldering
This process melts solder to form reliable connections between component leads and PCB pads. Reflow soldering is a specific step in the SMT process, where inert gas (typically nitrogen) is circulated in the reflow oven to create a high-temperature atmosphere, remelting the solder paste applied to the pads, and then cooling it to solidify. Vacuum reflow soldering equipment also exists. Since reflow soldering can only solder one side at a time, double-sided SMT requires two passes through the reflow oven. Because the solidification temperature of solder paste is higher than the reflow temperature, components on the reverse side do not detach during the second pass.
Reflow soldering is the stage where defects are most easily detected, though the root cause may not lie in the reflow process itself. Issues may arise from solder paste printing, placement, or the solderability of the PCB or component surfaces, but they only become apparent after reflow. The animation below illustrates a defect formation process: during solder melting, uneven tension on both sides of a component causes it to stand up, resulting in an open circuit. This could be due to poor solder paste printing or improper component placement.
The most critical aspect of reflow soldering is the temperature profile. For example, during preheating, flux begins to evaporate. If the temperature rises too quickly without allowing sufficient time for gas escape before moving to the soldering and cooling stages, solder voids may form, leading to defects. The diagram below shows a typical reflow temperature profile.
Solder paste datasheets usually provide recommended temperature profiles. Debugging the temperature profile requires temperature sensors/lines, calibrated thermometers, and PCB or assembly boards. SMT engineers must repeatedly test the temperature profile based on the solder paste datasheet, using temperature measurement devices and actual assembly boards. The more adjustable temperature zones available, the better the temperature profile can be optimized.
c. Component Soldering - Through-Hole Components
SMT is only suitable for surface-mount devices (SMDs). For through-hole components (PTH), other soldering processes are required.
c1. Wave Soldering
This process involves melting solder bars at high temperatures to form liquid solder, creating a specific wave shape on the surface of the solder bath. PCBs with inserted components are placed on a conveyor and passed through the solder wave at a specific angle and immersion depth to form solder joints.
Unlike reflow soldering, which heats from above with hot air, wave soldering uses solder waves from below. Disadvantages of wave soldering include:
No components should be near the solder joints on the soldering side, as the solder wave is broad and may cause component displacement.
Components on the soldering side are susceptible to thermal shock.
PCBs are prone to warping due to thermal shock.
Significant solder waste occurs if the line stops, as the solder bath contains large amounts of molten solder.
Wave soldering comes in two forms: single-wave and dual-wave.
For single-wave soldering, only one flat wave is used.
For dual-wave soldering, the first wave is called the turbulent wave, and the second is the flat wave.
Turbulent Wave:
The turbulent wave can mostly complete soldering. The solder in this wave moves actively at high speed through narrow gaps, ensuring even distribution. However, it may leave uneven or excessive solder on joints, necessitating a second wave—the flat wave.
Flat Wave:
The entire wave surface remains nearly level, resembling a mirror. While it appears static, the solder is continuously flowing, just very smoothly. Its function is to help eliminate solder spikes and shorts created by the turbulent wave.
c2. Selective Wave Soldering (SWS)
The SWS process is similar to wave soldering: board loading → flux spraying → preheating → soldering → cooling → board unloading. The key differences from wave soldering are:
Disadvantage: Lower efficiency compared to traditional wave soldering when there are many solder joints.
c3. Through-Hole Reflow (THR)
THR allows through-hole components to undergo solder paste printing, placement, and reflow soldering alongside SMDs.
Advantage: Eliminates the need for a separate soldering process, as it integrates with SMT.
Disadvantage: Standard PTH components may not withstand high temperatures, whereas THR components must endure higher temperatures (reflow soldering peaks around 250–260°C), increasing material costs.
c4. Automated Spot Soldering
This process mimics manual soldering using automated machinery, with robotic arms and temperature-controlled soldering. Programming is required to define soldering paths, temperatures, and durations.
d. PCB Depaneling - Routing/Punch/V-Cut
To improve production efficiency, PCBA are manufactured in panel form until depaneling, after which they are processed as individual boards.
d1. Manual Breakaway
Often used in the initial sample stage to save on tooling costs. Stress is high, and the PCB must be designed with breakaway tabs (mouse bites) for manual separation.
d2. Punch Depaneling
A die punches down onto the PCB to cut it apart.
Advantages: Low equipment cost, fast speed, and high efficiency.
Disadvantages: High die cost, as each PCB design requires a custom die.
Stress is very high for rigid boards, potentially damaging components.
More suitable for flexible boards, which are not prone to stress issues.
d3. V-Cut Depaneling
Advantages: Low cost, inexpensive equipment, and minimal tooling required.
Disadvantages: Only suitable for straight-line cuts, may leave burrs, and requires V-grooves on the PCB.
d4. Routing Depaneling
The most common method for rigid PCBs, using milling cutters.
Advantages: Can cut any shape, minimal stress, and clean edges without burrs.
Disadvantages: High equipment cost. Tooling for positioning and covering components is inexpensive, but milling cutters are consumables that wear out quickly.
d5. Laser Depaneling
Advantages: Offers the benefits of routing depaneling and can perform micro-cuts with no stress.
Disadvantages: High equipment cost.
e. On-Board Programming (OBP)
If IC components are mounted on the PCBA, programming may be required to load firmware into the ICs. Programming software is typically provided by the customer.
02 ABC Sharing Session - Logistics Handling Operations
Board Loading/Unloading/Transfer/Buffering
Traditional board loading: Manual, with one operator responsible for labeling and loading.
Automated board loading: Automatic labeling and loading.
Given efficiency and rising labor costs, more companies are adopting automated board handling, leading to the development of complete PCB loading/unloading/transfer/buffering systems. These systems consist of multiple devices, such as:
Multi Magazine Loader: Multi-layer board loader
Turn Conveyor: Board turning conveyor
Destacker: Board destacker
High-Speed Laser Marking: High-speed laser marking machine
Work Station: Operator workstation
FIFO Buffer: First-in-first-out buffer
Dual Unloader: Dual board unloader
03 ABC Sharing Session - Quality Control Operations
a. Incoming Quality Control (IQC)
When components arrive, they must undergo full or sampling inspection before being accepted into inventory. The entire receiving process is traceable, using barcodes or QR codes on component packaging to track receipt dates, inspection reports, and even supplier batch information.
Different components require different inspection criteria and equipment. Common inspection items include:
PCBs: Sampling for dimensions, with 100% full inspection for initial batches.
Electronic Components (resistors, capacitors, diodes, ICs, etc.): Sampling for resistance/capacitance values.
Connectors: Sampling for impedance.
Cables/Harnesses: Sampling for impedance.
Mechanical Parts: Sampling for dimensions, with 100% full inspection for initial batches.
Tips: How to Read Incoming Material Information?
Component labels contain various details that may seem overwhelming at first, but careful review reveals valuable information. For example, from the label below, we can identify:
CPN: Customer Part Number, the customer's part number.
QTY: Quantity, the quantity supplied. Resistors and capacitors often come in reels of 3,000 or 5,000 pieces.
DC: Date Code, indicating production date. For instance, "1638" means the 38th week of 2016.
B/C: Batch Code, used by the manufacturer for internal traceability, especially during quality issues.
MPN: Manufacturer Part Number, the original manufacturer's part number.
QR Code: Contains traceability information from the manufacturer.
RoHS: An environmental compliance mark. RoHS is a European Union directive restricting hazardous substances in electrical and electronic equipment.
YAGEO: Original manufacturer name (not the distributor).
Tips: How to Decode MPN?
Visit the component manufacturer's website to access the datasheet and check MPN naming rules.
Search for "MPN" or "PN" to quickly find the section explaining the coding rules.
Example: RC0603FR–0768RL
RC: Series code.
0603: Size code, indicating 0.06" × 0.03".
F: Resistance tolerance. YAGEO defines: B=±0.1%, D=±0.5%, F=±1.0%, J=±5%.
R: Packaging type.
–: Temperature coefficient of resistance; "–" indicates per detailed specifications.
07: Reel diameter, where "07" means 7 inches.
68R: Resistance value, 68 ohms.
L: Default system code.
b. Labeling for Traceability
Includes traceability during production and afterward. At each production station, the PCB label is scanned to promptly intercept defects, preventing faulty products from reaching the customer.
Common labeling methods include:
Label/print/engraving content may include text, barcodes, or QR codes.
The content (text/barcode/QR code) varies by company but generally includes part numbers, batch numbers, date codes, etc.
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