Technical
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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
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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
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Classification of PCBs from three aspects
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Several Elements to Inspect after PCB Design
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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
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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
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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

Reflow soldering stage in the BGA assembly process

On the production line of the SMT assembly plant, reflow soldering is a difficult process in the BGA assembly process. Setting process parameters and obtaining a suitable temperature profile are very important for good BGA soldering. Due to the different packaging forms of BGA, the thermal resistance of CBGA is larger than that of PBGA, so to reach the same temperature, CBGA requires a higher temperature setting and longer preheating time than PBGA. For tin-lead solder paste and lead-free solder paste, the temperature setting and heating time are significantly different.

1. Pre-heating stage

The main purpose of preheating is to heat the PCB and its components uniformly, and at the same time have a baking effect on the PCB and components, remove the moisture in it, and evaporate the appropriate amount of flux in the solder paste. The heating rate in the preheating stage cannot be too fast to prevent the PCB from being heated too fast and causing greater deformation. Generally, the heating rate is controlled at 3℃/s, and the preheating time is between 60-90s.

2. Activation stage

The main purpose of this stage is to activate the flux in the solder paste, remove the oxides on the surface of the pad and the surface of the solder paste alloy, to achieve a clean metal surface and prepare for the solder paste reflow process. At the same time, the excessive flux in the solder paste is evaporated and the PCB is preheated to prevent the PCB from deforming due to excessive heating during the reflow process. For tin-lead soldering, the temperature at this stage should be kept at 60-120S at 150-180℃; for lead-free soldering, the temperature at this stage should be kept at 60-180S at 160-200℃, so that the flux can fully play its role. The temperature rise rate in the activation stage is generally controlled at 0.3 plus. 5°C/s.


3. Reflow stage

At this stage, the temperature of the solder joint has risen above the melting point of the solder paste, and the solder paste is in a molten state. The main purpose of the reflow stage is to wet the solder pads and the pins of the components to achieve good soldering requirements. For PBGA, the solder balls are Sn63Pb37, Sn62Pb36Ag2, and Sn96.5Ag3.0Cu0.5 alloys. During the reflow process, the solder balls and solder paste are melted and mixed to form solder joints; for CBGA, the solder balls are Snl0Pb90 high-temperature alloys. The solder ball does not melt during the reflow process, the solder paste melts and wets the pad and the high-temperature solder ball to form a solder joint. Therefore, it takes a suitable time to ensure that the molten solder paste can well wet the pads and solder balls. Too short a time may cause poor wetting to form a pseudo solder, and too long may cause a thick formation between the solder and the pad, a layer of intermetallic compounds Cu6sn5 and Cu3Sn, due to its brittleness, is easy to form cracks and cause solder joint failure. Especially for lead-free electronic assembly, due to the high content of element Sn in lead-free solder alloying, it is easier to form thicker intermetallic compounds at high temperature and cause the failure of solder joints. For SnPb soldering, the time above the melting point of 183℃ is generally controlled in 60-90s, where the peak temperature is within the range of 210-225°C and the time is controlled within 10-20s; for lead-free soldering, it is generally required to control the time above the melting point of 217-219°C within 60-120s, and the peak temperature 230-235℃ is better to control the time in the range of 20-40s.


4. Cooling stage

After the solder paste is reflowed, the flux is completely consumed, forming a molten metal solder joint. The main purpose of the cooling stage is to refine the crystal grains while the solder joints are solidified, inhibit the growth of intermetallic compounds, and improve the strength of the solder joints. However, too fast cooling rate will cause PCB deformation and thermal cracking of electronic components, especially for components with large heat absorption such as BGA, too fast cooling rate will easily cause damage to the internal package, leading to BGA failure. Generally, the cooling rate is controlled within 1-3℃/s.