1. In an automatic surface mount line, if the circuit board is not flat, it can lead to inaccurate positioning, preventing components from being properly inserted or mounted onto the board’s holes and surface mount pads. In some cases, the automatic mounter itself may even be damaged.
2. Once the circuit board is populated with components, any warping can make it difficult to trim component leads flush. Additionally, the board may not fit properly into its case or socket. As a result, PCB assembly plants often face challenges related to board warping.
3. Current surface mount technology is evolving toward higher precision, faster speeds, and greater intelligence, which requires PCBs to exhibit superior flatness and serve as stable substrates for a wide range of components.
4. Specifically, the IPC standard specifies that the allowable warpage for PCBs with surface mount devices (SMDs) is 0.75%, while for PCBs without surface mount devices, the allowable warpage is 1.5%.
5. In practical applications, to meet the demands of high-precision and high-speed placement, some electronics manufacturers impose even stricter deformation limits, such as 0.5%, or in certain cases, as low as 0.3%.
6. A printed circuit board consists of copper foil, resin, glass fabric, and other materials, each with different physical and chemical properties. When pressed together, these materials inevitably generate thermal stresses that can lead to deformation.
7. Additionally, during the manufacturing process, the PCB undergoes various stages, including high-temperature exposure, mechanical cutting, and wet processing, all of which can significantly affect the board’s deformation. The causes of PCB deformation are complex and multifaceted. Finding ways to reduce or eliminate warping due to varying material properties and processing techniques has become a key challenge for PCB manufacturers.
2. **Uses of Circuit Board Deformation**
Deformation of printed circuit boards (PCBs) needs to be studied from multiple perspectives, including materials, structure, pattern distribution, and processing techniques. This article will analyze the various causes and methods of improvement for PCB deformation.
Uneven copper distribution on the board leads to increased bending and warping.
Typically, a large amount of copper foil is used on the circuit board for grounding, and sometimes also on the Vcc layer. When this copper is not evenly distributed, heat absorption and dissipation issues arise, leading to uneven thermal effects.
The circuit board itself is heat-sensitive, and if heat-shrinkage causes uneven stress and deformation, the board will soften once it reaches the upper limit of its Tg (glass transition temperature), resulting in warping.
The connections between layers on the PCB, such as vias, also restrict board movement.
Modern circuit boards are often multi-layer designs, with connections between layers resembling rivets. These include through-holes, blind holes, and buried holes. These joints restrict the expansion and contraction of the board, indirectly causing bending and warping.
**Causes of PCB Deformation:**
The weight of the PCB itself can lead to denting and deformation.
In reflow ovens, the board is typically moved forward via a chain structure, with the edges of the board acting as the fulcrum. If the board has heavy components or is oversized, the middle may sag due to its own weight, causing bending.
The depth of V-Cuts and the connecting strips can influence the deformation of the board.
V-Cuts are the main structural weaknesses of a PCB because they are grooves cut into the original board. This makes the PCB more prone to deformation at the V-Cut areas.
**Impact of Crimping Materials, Structure, and Patterning on Deformation:**
PCBs are made by pressing a core board, prepreg, and outer copper foil together. During the pressing process, both the core and copper foil undergo deformation due to heat. The degree of deformation depends on the coefficient of thermal expansion (CTE) of the materials involved.
The CTE of copper is around 17 × 10⁻⁶, while the CTE of FR-4 (a common PCB substrate) is approximately (50-70) × 10⁻⁶. The CTE in the X-direction of ordinary FR-4 is typically similar to copper foil due to the presence of glass fiber.
3. **Deformation During PCB Processing**
The causes of deformation during PCB manufacturing are complex, with both thermal and mechanical stresses playing a role. Below is an overview of deformation causes, categorized by process.
1. **Copper-Clad Raw Materials:**
Copper-clad laminates are double-layer panels with a symmetrical structure and no patterns. Since the CTEs of copper foil and glass cloth are quite different, deformation due to this CTE mismatch is uncommon during lamination. However, because copper-clad laminate presses are large and have temperature variations across the hot plate, there can be slight differences in resin curing speeds across the press. Additionally, dynamic viscosity changes with different heating rates, leading to local curing stress during the process.
In most cases, stress is balanced after pressing, but it may gradually be released during subsequent processing, causing deformation.
2. **Pressing:**
The lamination process is the primary source of thermal stress in PCB manufacturing. Similar to copper-clad laminates, localized stress can result from variations in the curing process. Since printed circuit boards are thicker and have more complex patterns than copper-clad laminates, the prepreg material makes it more difficult to eliminate thermal stress.
Furthermore, stress can be released during subsequent operations like drilling, forming, or baking, leading to further deformation.
3. **Processes such as Solder Mask and Character Baking:**
Solder mask inks cannot overlap during curing, so circuit boards are placed on racks for curing. Solder mask curing temperatures typically range around 150°C, which is close to the Tg point of the material. When the resin reaches this temperature, it becomes highly elastic, making the board prone to deformation under its own weight or the force of airflow in the oven.
4. **Hot-Air Soldering Flatness:**
The temperature of the tin furnace in hot-air solder leveling machines typically ranges from 225°C to 265°C, with a time window of 3 to 6 seconds. The hot air temperature itself ranges from 280°C to 300°C. When the PCB is transferred from room temperature to the tin furnace, and subsequently undergoes room-temperature water washing within two minutes, this rapid cooling process can cause thermal stress.
Due to the differing materials and structures within the PCB, these thermal stresses can result in microscopic strains and cause overall warping.
5. **Storage:**
PCBs are often stored in a semi-finished state on shelves. If the shelves are not properly adjusted, or if boards are improperly stacked or stored, mechanical deformation can occur. This is especially true for boards under 2.0mm thick.
Aside from the factors mentioned above, there are many other influences on PCB deformation during storage.
4. **Preventing Warping and Deformation of Circuit Boards**
The warping of PCBs has a significant impact on the production process. Deformation can affect the placement and alignment of components after soldering, making it difficult to properly position component leads. Additionally, warpage can prevent the board from fitting correctly into a chassis or socket, negatively impacting the functionality of the finished product. Therefore, preventing deformation is crucial for ensuring the proper operation of subsequent processes and the final product.
2. Once the circuit board is populated with components, any warping can make it difficult to trim component leads flush. Additionally, the board may not fit properly into its case or socket. As a result, PCB assembly plants often face challenges related to board warping.
3. Current surface mount technology is evolving toward higher precision, faster speeds, and greater intelligence, which requires PCBs to exhibit superior flatness and serve as stable substrates for a wide range of components.
4. Specifically, the IPC standard specifies that the allowable warpage for PCBs with surface mount devices (SMDs) is 0.75%, while for PCBs without surface mount devices, the allowable warpage is 1.5%.
5. In practical applications, to meet the demands of high-precision and high-speed placement, some electronics manufacturers impose even stricter deformation limits, such as 0.5%, or in certain cases, as low as 0.3%.
6. A printed circuit board consists of copper foil, resin, glass fabric, and other materials, each with different physical and chemical properties. When pressed together, these materials inevitably generate thermal stresses that can lead to deformation.
7. Additionally, during the manufacturing process, the PCB undergoes various stages, including high-temperature exposure, mechanical cutting, and wet processing, all of which can significantly affect the board’s deformation. The causes of PCB deformation are complex and multifaceted. Finding ways to reduce or eliminate warping due to varying material properties and processing techniques has become a key challenge for PCB manufacturers.
2. **Uses of Circuit Board Deformation**
Deformation of printed circuit boards (PCBs) needs to be studied from multiple perspectives, including materials, structure, pattern distribution, and processing techniques. This article will analyze the various causes and methods of improvement for PCB deformation.
Uneven copper distribution on the board leads to increased bending and warping.
Typically, a large amount of copper foil is used on the circuit board for grounding, and sometimes also on the Vcc layer. When this copper is not evenly distributed, heat absorption and dissipation issues arise, leading to uneven thermal effects.
The circuit board itself is heat-sensitive, and if heat-shrinkage causes uneven stress and deformation, the board will soften once it reaches the upper limit of its Tg (glass transition temperature), resulting in warping.
The connections between layers on the PCB, such as vias, also restrict board movement.
Modern circuit boards are often multi-layer designs, with connections between layers resembling rivets. These include through-holes, blind holes, and buried holes. These joints restrict the expansion and contraction of the board, indirectly causing bending and warping.
**Causes of PCB Deformation:**
The weight of the PCB itself can lead to denting and deformation.
In reflow ovens, the board is typically moved forward via a chain structure, with the edges of the board acting as the fulcrum. If the board has heavy components or is oversized, the middle may sag due to its own weight, causing bending.
The depth of V-Cuts and the connecting strips can influence the deformation of the board.
V-Cuts are the main structural weaknesses of a PCB because they are grooves cut into the original board. This makes the PCB more prone to deformation at the V-Cut areas.
**Impact of Crimping Materials, Structure, and Patterning on Deformation:**
PCBs are made by pressing a core board, prepreg, and outer copper foil together. During the pressing process, both the core and copper foil undergo deformation due to heat. The degree of deformation depends on the coefficient of thermal expansion (CTE) of the materials involved.
The CTE of copper is around 17 × 10⁻⁶, while the CTE of FR-4 (a common PCB substrate) is approximately (50-70) × 10⁻⁶. The CTE in the X-direction of ordinary FR-4 is typically similar to copper foil due to the presence of glass fiber.
3. **Deformation During PCB Processing**
The causes of deformation during PCB manufacturing are complex, with both thermal and mechanical stresses playing a role. Below is an overview of deformation causes, categorized by process.
1. **Copper-Clad Raw Materials:**
Copper-clad laminates are double-layer panels with a symmetrical structure and no patterns. Since the CTEs of copper foil and glass cloth are quite different, deformation due to this CTE mismatch is uncommon during lamination. However, because copper-clad laminate presses are large and have temperature variations across the hot plate, there can be slight differences in resin curing speeds across the press. Additionally, dynamic viscosity changes with different heating rates, leading to local curing stress during the process.
In most cases, stress is balanced after pressing, but it may gradually be released during subsequent processing, causing deformation.
2. **Pressing:**
The lamination process is the primary source of thermal stress in PCB manufacturing. Similar to copper-clad laminates, localized stress can result from variations in the curing process. Since printed circuit boards are thicker and have more complex patterns than copper-clad laminates, the prepreg material makes it more difficult to eliminate thermal stress.
Furthermore, stress can be released during subsequent operations like drilling, forming, or baking, leading to further deformation.
3. **Processes such as Solder Mask and Character Baking:**
Solder mask inks cannot overlap during curing, so circuit boards are placed on racks for curing. Solder mask curing temperatures typically range around 150°C, which is close to the Tg point of the material. When the resin reaches this temperature, it becomes highly elastic, making the board prone to deformation under its own weight or the force of airflow in the oven.
4. **Hot-Air Soldering Flatness:**
The temperature of the tin furnace in hot-air solder leveling machines typically ranges from 225°C to 265°C, with a time window of 3 to 6 seconds. The hot air temperature itself ranges from 280°C to 300°C. When the PCB is transferred from room temperature to the tin furnace, and subsequently undergoes room-temperature water washing within two minutes, this rapid cooling process can cause thermal stress.
Due to the differing materials and structures within the PCB, these thermal stresses can result in microscopic strains and cause overall warping.
5. **Storage:**
PCBs are often stored in a semi-finished state on shelves. If the shelves are not properly adjusted, or if boards are improperly stacked or stored, mechanical deformation can occur. This is especially true for boards under 2.0mm thick.
Aside from the factors mentioned above, there are many other influences on PCB deformation during storage.
4. **Preventing Warping and Deformation of Circuit Boards**
The warping of PCBs has a significant impact on the production process. Deformation can affect the placement and alignment of components after soldering, making it difficult to properly position component leads. Additionally, warpage can prevent the board from fitting correctly into a chassis or socket, negatively impacting the functionality of the finished product. Therefore, preventing deformation is crucial for ensuring the proper operation of subsequent processes and the final product.
