Technical
How to Judge the Acceptance of PCB Quality
Which Color Circuit Board Sells the Most Expensive
Method to Solve the Noise Interference of Power Supply on High-frequency PCB Board
Disassembly Skills of Chip Components on PCB
What Factors Should Be Considered in the Selection of High-frequency PCB CCL
How to Place Special Components during PCB Layout
What Are the Functions of Capacitors in Circuits?
Testing Techniques for Common Electronics Components
What to do if There is a Short Circuit on the PCB
Desoldering Principles and knowhow during PCBA Processing
Black Oxidation of the Inner Layer of the Multilayer PCB
How to Ensure the High-performance Design of PCB
What Is the Printing Process of SMT Solder Paste?
PCB without fiducial mark, Is There Any Way to do SMT for It
What Are the Benefits of Reserving Break-up Tab for PCB Production
How Does SMT Affect PCB Production Time and Speed It Up
Classification of PCBs from three aspects
Common Problems and Solutions for Dry Film pasting during PCB Manufacturing process
Several Elements to Inspect after PCB Design
What is a halogen-free circuit board?
What Do Capacitive Coupling and Decoupling Mean?
What Are the Differences Between PCB Paste Mask and Solder Mask?
How PCBA Is Packaged and Shipped
How long can PCBA finished products be stored?
What Are the Differences and Relations Between PCB, PCBA, and SMT?
PCB Baking Specifications
PCB "Solder Mask Tenting" and "Solder Mask Opening"
Five reasons for PCB deformation and six solutions
Importance of first article inspection of PCBA board
Temperature zone standard for SMT reflow soldering
Small and medium volume PCB manufacturers in China
The main reason for PCBA cleaning
For power filter, the more capacitors, the better?
What does PCBA programming mean?
Content of PCB incoming testing
What conditions must be met for PCB circuit board soldering?
What is Blind via and Buried via
PCBA Manufacturers Temperature and Humidity Sensitive Components Management
Why choose Shenzhen SMT processing factory?
How long does it take to calculate the quotation for PCBA manufacturing?
Introduction of PCB design clearance requirements
Explanation of BOM, DIP, SMT, SMD
Introduction of the process of PCBA prototype
How to prevent pseudo soldering or cold soldering defects in PCBA manufacturing?
Factors that affect the Price of FPCB
What information is required for SMT processing at PCBA factory?
Skills of using 0ohm resistor in PCB design
How to select a PCBA manufacturer
SMT processing solder joint quality inspection
Characteristics difference between immersion gold PCB and gold plating PCB
Common malfunctions of Circuit Board Caused by Moisture
A Few Rules about PCB Panelization
Compare of multi-layer PCB with single/double layer PCB
Why do we need to introduce so many subdivided GND
Difference between immersion gold boards and gold plating boards
Aluminum PCB structure
Classification of different GND in circuit
Why PCB baking is necessary during manufacturing process
The handle and precautions of OSP board in SMT process
How to choose capacitors for filter decoupling
How to choose filter capacitor for switching power supply
5 database need for SMT process
Function of three-terminal capacitor
Introduction of PCB OSP surface treatment
Method of inspecting the quality of SMT by step
How to find the short point between VCC and GND
Difference between 850nm and 940nm infrared LED
Component layout of PCB SMT DFM
Pad shape influence on the strength and reliability of the soldering joints
The difference between high temperature solder paste and low temperature solder paste
Introduction to manual welding processing
Manual visual inspection in PCBA processing
Characteristics of the conformal coating process
Difference between hardware engineers and software engineers
PCBA processing operation rules
China PCB upstream materials has continued to soar
Difference between serial buses and parallel buses
The key points of quality control in PCBA processing
Common causes of solder beading during SMT process
Analysis of the advantages and disadvantages of HASL PCB surface
Requirements for layout of components during SMT assembly
Selection of electronic components and CCL for PCBA
Performance and appearance quality inspection of components.
Quality and Reliability of SMT Chip Processing and Production
Coupling and decoupling function of capacitor
Two methods to connect digital ground and analog ground
Common sense in SMT process

Quality and Reliability of SMT Chip Processing and Production

SMT technology is an electronic assembly technology with a very high degree of automation. With the development of miniaturization of electronic products, a fundamental revolution has taken place in the SMT production process. At present, in the production and assembly of SMT processing plants, there are 4types of SMT production, single-sided SMT, single-sided SMT assembly hybrid with through-hole soldering, double-sided SMT, double-sided SMT assembly hybrid with through-hole soldering. This article will continue the introduction of "Quality and Reliability of SMT Chip Processing and Production".

3. Process parameters during reflow soldering
Controlling of reflow soldering is generally divided into three stages: preheating stage, heat preservation stage and reflow stage. Before reflow soldering, it is necessary to set the temperature of these three stages, and determine the temperature curve of each production, so as to ensure the high reliability of each production. According to the requirements of the reflow soldering equipment, combined with the specifications and parameters of the solder paste, develop more ideal temperature profile.

1) Process parameter control in the preheating stage
The purpose of preheating is to heat the printed circuit board from room temperature to the desired temperature for activating the solder paste, but the heating rate must be controlled within an appropriate range. If it is too fast, thermal shock will occur to the circuit board and components. For example, some components are sensitive to internal stress, if the external temperature of the component rises too fast, it may be damaged.
If it is too slow, the solvent in the solder paste will not evaporate sufficiently and affect the quality of soldering. After analysis and repeated practice, it is believed that the heating rate of 3℃/s in the preheating zone is the most appropriate, and the preheating effect is best when the temperature rises to 180℃. In this way, a good preheating effect can be obtained, and it can also effectively limit boiling and splashing, and prevent the formation of small solder beads.

2) Process parameter control in the heat preservation stage
The heat preservation stage refers to the area where the temperature rises to the melting point of the solder paste, which generally occupies 33% to 50% of the heating channel. Provide enough time in this area for the temperature of larger components to catch up with smaller components. The main purpose of this stage is to stabilize the temperature of each component on the printed board, close to the melting point of the solder paste, and minimize the temperature difference. Make it easier to transition to the reflow stage; another purpose of this area is to activate the flux in the solder paste to make it fully volatilized, remove the oxide on the pad and the lead, and leave a clean surface where the solder can adhere. The applicable temperature range of the heat preservation stage is 120℃~180℃. If the temperature is set too high, the flux will not have enough time to activate, which will eventually affect the soldering effect.

3) Process parameter control in the reflow stage
The temperature of the reflow stage is set to the highest among the process, its function is to increase the temperature of the printed board from the active temperature to the peak temperature, so that the solder paste, the pad and the lead can form a eutectic alloy layer. For example, in tin-lead soldering, the alloy is Sn63/Pb37. The eutectic tin-lead alloy has a single melting point of 183°C, the typical temperature range of the reflow stage is 205°C to 220°C. 
Setting the temperature too high in the reflow stage will cause warpage, delamination or burnout of the printed board, and will damage the integrity of the component. The ideal temperature setting is to minimize the area that exceeds the melting point of the solder. The printed boards sent to the conveyor belt of the reflow oven go through preheating, heat preservation, and reflow stages in sequence without interruption. It takes about 4 minutes. After natural cooling, the soldered printed boards can be obtained from the conveyor belt exit.

4) Speed control of hot air convection fan
Increasing the convective thermal conductivity can increase the amount of heat transferred from the heat source to the PCB. As the heat transfer speed increases, the time for the PCB to reach the same final temperature can be shortened, thereby increasing the speed of the conveyor belt. If the speed of the conveyor belt is kept constant, the set temperature of the heating zone can be lowered, thereby reducing energy consumption.

4. SMT Production quality process control
Familiarity with the quality inspection process is the key to improving the quality and reliability of SMT products.
In order to ensure the normal operation of SMT processing and production, it is necessary to strengthen the quality inspection of the processed PCBA in each process to monitor its operating status. Therefore, it is necessary to set up quality control points after some key processes, so that quality problems in the previous process can be found and corrected in time. Prevent unqualified PCBA products from entering the next process and reduce the economic loss caused by quality defect to a minimum. The setting of the quality control point is related to the specific production.

5 Conclusion
"Reliability" is the ability of an electronic product to maintain its function within a specified time. One is the continuation of product quality with the time; the second is the anti-interference ability of the product; the third is the natural quality characteristics of the product. It is measured by high reliability, high stability, and high consistency. In surface assembly technology, the quality assurance of solder joints is the most important. This involves all aspects of the problem, we must work hard on quality management to minimize various factors that affect the quality of solder joints, so as to provide good quality assurance and improve the overall reliability of electronic products.