With the rapid development of the electronics industry, some large-scale electronic processing companies, from the initial Pearl River Delta to the Yangtze River Delta, and even to the current Jinjing and Bohai Rim areas, SMT has become the mainstream, from the earliest hand patch to the current automation Most of the device patches are made using SMT solder paste technology, but many companies have products that cannot be avoided (such as computer monitors). Therefore, the earlier red glue process and the emergence of the later Kong Bo peak welding process. However, the production of red rubber craft has very strict requirements for the control of wave soldering and the design of PCB's manufacturability. In the following, I only introduce a series of requirements for the design, process parameters, etc. of the printed red rubber process. It is through our company - Shanghai. Chang Xiang Industrial - Many world-class customers have experimented with effective experience and a total of SMT industry references.
Customers through the test of visual intercom products, from the device packaging, socket packaging, reasonable device layout design, technical requirements of the template hole opening, reasonable adjustment of wave soldering parameters, PCB board one-time pass rate of 92 % or more (There are six 20-pin ICs and one 48-pin QFP on this product). After the wave soldering, only a minor repair can achieve a 100% pass rate, but the welding efficiency is improved by more than 3 times compared to manual soldering.
The following are some of the specific design requirements that Shanghai Changxiang Industrial Co., Ltd. summarized based on the practices of our customers, shared to SMT counterparts:
One for template thickness and opening requirements
(1) Template thickness: 0.2mm
(2) Template opening requirements: The opening width of the IC is 1/2 of the width of the two pads, and multiple small round holes can be opened.
Two device layout requirements
(1) The long axis of the Chip element is perpendicular to the direction of the conveyor belt of the wave soldering machine; the long axis of the integrated circuit device should be parallel to the belt direction of the wave soldering machine.
(2) In order to avoid the shadow effect, the ends of the same size components are aligned in a direction parallel to the direction of the solder wave; different size components should be staggered; small components should be arranged in front of large components; prevent components Body shields solder tips and pins. When the above requirements cannot be arranged, 3~5mm spacing should be left between the components.
(3) The characteristic directions of the components should be consistent. For example, the polarity of the electrolytic capacitor, the anode of the diode, and the single-pin end of the transistor should be perpendicular to the transmission direction, the first leg of the integrated circuit, and the like.
Three-element aperture and pad design
(1) The component holes must be arranged in the basic grid, 1/2 basic grid, and 1â„4 basic grid. The gap between the pad holes and the pin diameter of the interposing component is such that the solder wets well.
(2) The elliptical pad pattern should be used when wiring high-density components to reduce the solder connection.
Four Wave Soldering Process Basic Requirements for Components and Printed Boards
(1) Three-layer surface-mount surface-mount components should be selected, and the body and the solder tail can withstand temperature shocks of more than two wave solders at 260 degrees Celsius. The body of the device after soldering is not damaged or deformed, and the tip of the chip element is not capped off.
(2) The substrate should be able to withstand the heat resistance of 260 degrees Celsius / 50s. The copper foil has good peel strength, and the solder mask still has sufficient adhesion at high temperatures, and the solder mask does not wrinkle after soldering.
(3) Board warpage less than 0.8-1.0%
Five wave soldering parameters design
(1) Flux system: The amount of blowing air or the spray pressure of the flux is determined according to the situation where the flux contacts the bottom of the PCB: The amount of sprayed flux is required to have a uniform and thin layer at the bottom of the printed board, flux coating method There are brushing foaming and quantitative spray two.
A. The use of coating and foaming methods must control the specific gravity of the flux. The specific gravity of flux is generally controlled between 0.8 and 0.83.
B When using the quantitative injection method, the flux is sealed in the container, will not volatilize, will not absorb the moisture in the air, will not be contaminated, so the flux composition can remain unchanged. The key requirement is that the nozzles can control the amount of spray. The nozzles should be cleaned frequently and the injection holes cannot be blocked.
(2) Preheating temperature: It is set according to the actual situation of wave soldering machine preheating zone (90-130 degrees Celsius).
Preheating function: volatilize the solvent in the flux, which can reduce the gas generated during welding; the rosin and the active agent in the flux begin to decompose and activate, and the PCB pad, component terminals and pins can be removed. The surface oxide film and other contaminants also protect the metal surface from re-oxidation; allow the printed board and components to be fully preheated, avoiding rapid temperature rise during soldering, and thermal stress damage to the printed board and components.
Welding temperature and time: The welding process is a complex process of interaction between the weld metal surface, molten solder and air, etc. The welding temperature and time must be controlled. If the soldering temperature is low, the viscosity of the liquid solder is too large to allow good wetting and diffusion on the surface of the metal, resulting in defects such as tipping, bridging, and rough soldering surfaces. If the soldering temperature is too high, the components may be easily damaged. There will be problems such as the accelerated oxidation rate of solder joints, the development of solder joints, and the lack of solder joints. The wave soldering temperature is determined according to the size and thickness of the printed board, the number of components on the printed board, and the size. The wave soldering temperature is generally 250±5°C. Since the heat is a function of temperature and time, the solder joints can be soldered at a certain temperature. The heat of components and heating increases with time. The welding time of wave soldering is controlled by adjusting the speed of the conveyor belt. The speed of the conveyor belt is adjusted according to the length of the wave soldering of different models and the width of the crest to contact each solder joint. The peak time represents the welding time, and the second wave soldering time is generally 2.5-4s. Board climbing angle and peak height: The board climbing angle is generally 3-7 degrees, and it is recommended 5.5-6 degrees. It helps to eliminate the gases that are generated by the flux around the solder joints and components. For example, if there are fewer through holes when designing with SMD, the climbing angle (inclination angle) should be larger. Appropriate climbing angle can avoid leakage welding and play an exhaust role; the peak height is generally controlled at the thickness of the printed board. 2/3 and 3/4.
(3) Comprehensive adjustment of wave soldering process parameters: This is very important for improving the quality of wave soldering. Welding temperature and time are the primary conditions for forming good solder joints. The welding temperature and time are related to the preheating temperature, tilt angle, and transmission speed. In order to comprehensively adjust the process parameters, the welding temperature and time must be guaranteed. The first peak of lead dual wave soldering is generally around 220-230 degrees Celsius/1s, the second peak is generally around 230-240 degrees Celsius/3s, and the total time of the two peaks is controlled around 4-7s. The copper content cannot exceed 1%. After the copper content increases, the surface tension of tin also increases and the melting point also increases. Therefore, it is recommended that wave soldering be used for copper once a month. The maintenance is to set the tin furnace at about 200 degrees. Waiting 4-8. After hours, remove copper-containing impurities (Cn6Sn5) on the tin surface.
Six red rubber selection and use
(1) Since it is not a dispensing process but a red glue process, there is a certain requirement for the thixotropic index and viscosity of red glue. If the thixotropic index and viscosity are not good, the molding after printing is not good, that is, the collapse phenomenon occurs. There will be some ICs that are not glued to red glue. (Reference thixotropic index: 4-5; reference viscosity: (2-6) x 1000000)
(2) The uncured adhesive stuck to the circuit board can be wiped off with acetone or propylene glycol ether or cleaned with a special cleaning agent for red glue.
(3) Store unopened products in a dry place at 2-10°C. The storage period is 6 months (based on the date of shipment from the package). Before use, return the product to room temperature and allow it to warm up for more than 24 hours.
(4) Select the curing time: 90-120 seconds, and the curing temperature is better around 150 degrees.
(5) To have good heat resistance and excellent electrical properties, as well as extremely low moisture absorption and high stability.
Seven printing machine parameter adjustment precautions
(1) The pressure is about 4.5 kg
(2) The amount of red glue to make the red glue rolling on the template is the best
(3) The distance in SNAP OFF is set to 0.05mm, and the speed is set to: 2 levels.
(4) The automatic wipe frequency is set to 2.
(5) Red plastic on the template after the end of production is scrapped when it is no longer used within 5 days
(6) The red glue must be accurately printed in the middle of the two lands and must not be offset.
Customers through the test of visual intercom products, from the device packaging, socket packaging, reasonable device layout design, technical requirements of the template hole opening, reasonable adjustment of wave soldering parameters, PCB board one-time pass rate of 92 % or more (There are six 20-pin ICs and one 48-pin QFP on this product). After the wave soldering, only a minor repair can achieve a 100% pass rate, but the welding efficiency is improved by more than 3 times compared to manual soldering.
The following are some of the specific design requirements that Shanghai Changxiang Industrial Co., Ltd. summarized based on the practices of our customers, shared to SMT counterparts:
One for template thickness and opening requirements
(1) Template thickness: 0.2mm
(2) Template opening requirements: The opening width of the IC is 1/2 of the width of the two pads, and multiple small round holes can be opened.
Two device layout requirements
(1) The long axis of the Chip element is perpendicular to the direction of the conveyor belt of the wave soldering machine; the long axis of the integrated circuit device should be parallel to the belt direction of the wave soldering machine.
(2) In order to avoid the shadow effect, the ends of the same size components are aligned in a direction parallel to the direction of the solder wave; different size components should be staggered; small components should be arranged in front of large components; prevent components Body shields solder tips and pins. When the above requirements cannot be arranged, 3~5mm spacing should be left between the components.
(3) The characteristic directions of the components should be consistent. For example, the polarity of the electrolytic capacitor, the anode of the diode, and the single-pin end of the transistor should be perpendicular to the transmission direction, the first leg of the integrated circuit, and the like.
Three-element aperture and pad design
(1) The component holes must be arranged in the basic grid, 1/2 basic grid, and 1â„4 basic grid. The gap between the pad holes and the pin diameter of the interposing component is such that the solder wets well.
(2) The elliptical pad pattern should be used when wiring high-density components to reduce the solder connection.
Four Wave Soldering Process Basic Requirements for Components and Printed Boards
(1) Three-layer surface-mount surface-mount components should be selected, and the body and the solder tail can withstand temperature shocks of more than two wave solders at 260 degrees Celsius. The body of the device after soldering is not damaged or deformed, and the tip of the chip element is not capped off.
(2) The substrate should be able to withstand the heat resistance of 260 degrees Celsius / 50s. The copper foil has good peel strength, and the solder mask still has sufficient adhesion at high temperatures, and the solder mask does not wrinkle after soldering.
(3) Board warpage less than 0.8-1.0%
Five wave soldering parameters design
(1) Flux system: The amount of blowing air or the spray pressure of the flux is determined according to the situation where the flux contacts the bottom of the PCB: The amount of sprayed flux is required to have a uniform and thin layer at the bottom of the printed board, flux coating method There are brushing foaming and quantitative spray two.
A. The use of coating and foaming methods must control the specific gravity of the flux. The specific gravity of flux is generally controlled between 0.8 and 0.83.
B When using the quantitative injection method, the flux is sealed in the container, will not volatilize, will not absorb the moisture in the air, will not be contaminated, so the flux composition can remain unchanged. The key requirement is that the nozzles can control the amount of spray. The nozzles should be cleaned frequently and the injection holes cannot be blocked.
(2) Preheating temperature: It is set according to the actual situation of wave soldering machine preheating zone (90-130 degrees Celsius).
Preheating function: volatilize the solvent in the flux, which can reduce the gas generated during welding; the rosin and the active agent in the flux begin to decompose and activate, and the PCB pad, component terminals and pins can be removed. The surface oxide film and other contaminants also protect the metal surface from re-oxidation; allow the printed board and components to be fully preheated, avoiding rapid temperature rise during soldering, and thermal stress damage to the printed board and components.
Welding temperature and time: The welding process is a complex process of interaction between the weld metal surface, molten solder and air, etc. The welding temperature and time must be controlled. If the soldering temperature is low, the viscosity of the liquid solder is too large to allow good wetting and diffusion on the surface of the metal, resulting in defects such as tipping, bridging, and rough soldering surfaces. If the soldering temperature is too high, the components may be easily damaged. There will be problems such as the accelerated oxidation rate of solder joints, the development of solder joints, and the lack of solder joints. The wave soldering temperature is determined according to the size and thickness of the printed board, the number of components on the printed board, and the size. The wave soldering temperature is generally 250±5°C. Since the heat is a function of temperature and time, the solder joints can be soldered at a certain temperature. The heat of components and heating increases with time. The welding time of wave soldering is controlled by adjusting the speed of the conveyor belt. The speed of the conveyor belt is adjusted according to the length of the wave soldering of different models and the width of the crest to contact each solder joint. The peak time represents the welding time, and the second wave soldering time is generally 2.5-4s. Board climbing angle and peak height: The board climbing angle is generally 3-7 degrees, and it is recommended 5.5-6 degrees. It helps to eliminate the gases that are generated by the flux around the solder joints and components. For example, if there are fewer through holes when designing with SMD, the climbing angle (inclination angle) should be larger. Appropriate climbing angle can avoid leakage welding and play an exhaust role; the peak height is generally controlled at the thickness of the printed board. 2/3 and 3/4.
(3) Comprehensive adjustment of wave soldering process parameters: This is very important for improving the quality of wave soldering. Welding temperature and time are the primary conditions for forming good solder joints. The welding temperature and time are related to the preheating temperature, tilt angle, and transmission speed. In order to comprehensively adjust the process parameters, the welding temperature and time must be guaranteed. The first peak of lead dual wave soldering is generally around 220-230 degrees Celsius/1s, the second peak is generally around 230-240 degrees Celsius/3s, and the total time of the two peaks is controlled around 4-7s. The copper content cannot exceed 1%. After the copper content increases, the surface tension of tin also increases and the melting point also increases. Therefore, it is recommended that wave soldering be used for copper once a month. The maintenance is to set the tin furnace at about 200 degrees. Waiting 4-8. After hours, remove copper-containing impurities (Cn6Sn5) on the tin surface.
Six red rubber selection and use
(1) Since it is not a dispensing process but a red glue process, there is a certain requirement for the thixotropic index and viscosity of red glue. If the thixotropic index and viscosity are not good, the molding after printing is not good, that is, the collapse phenomenon occurs. There will be some ICs that are not glued to red glue. (Reference thixotropic index: 4-5; reference viscosity: (2-6) x 1000000)
(2) The uncured adhesive stuck to the circuit board can be wiped off with acetone or propylene glycol ether or cleaned with a special cleaning agent for red glue.
(3) Store unopened products in a dry place at 2-10°C. The storage period is 6 months (based on the date of shipment from the package). Before use, return the product to room temperature and allow it to warm up for more than 24 hours.
(4) Select the curing time: 90-120 seconds, and the curing temperature is better around 150 degrees.
(5) To have good heat resistance and excellent electrical properties, as well as extremely low moisture absorption and high stability.
Seven printing machine parameter adjustment precautions
(1) The pressure is about 4.5 kg
(2) The amount of red glue to make the red glue rolling on the template is the best
(3) The distance in SNAP OFF is set to 0.05mm, and the speed is set to: 2 levels.
(4) The automatic wipe frequency is set to 2.
(5) Red plastic on the template after the end of production is scrapped when it is no longer used within 5 days
(6) The red glue must be accurately printed in the middle of the two lands and must not be offset.
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