CN117483893A - Accurate control method for SMT reflow soldering furnace temperature - Google Patents
Accurate control method for SMT reflow soldering furnace temperature Download PDFInfo
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- CN117483893A CN117483893A CN202311622284.3A CN202311622284A CN117483893A CN 117483893 A CN117483893 A CN 117483893A CN 202311622284 A CN202311622284 A CN 202311622284A CN 117483893 A CN117483893 A CN 117483893A
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- 238000005476 soldering Methods 0.000 title claims abstract description 82
- 238000000034 method Methods 0.000 title claims abstract description 57
- 238000001816 cooling Methods 0.000 claims abstract description 59
- 238000010438 heat treatment Methods 0.000 claims abstract description 42
- 230000008569 process Effects 0.000 claims abstract description 18
- 230000001276 controlling effect Effects 0.000 claims description 22
- 238000010992 reflux Methods 0.000 claims description 21
- 239000000523 sample Substances 0.000 claims description 15
- 230000000630 rising effect Effects 0.000 claims description 9
- 238000004088 simulation Methods 0.000 claims description 8
- 238000012360 testing method Methods 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 230000008859 change Effects 0.000 claims description 5
- 230000009471 action Effects 0.000 claims description 4
- 238000013459 approach Methods 0.000 claims description 3
- 238000005259 measurement Methods 0.000 claims description 3
- 230000001105 regulatory effect Effects 0.000 claims description 3
- 238000003466 welding Methods 0.000 description 44
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 16
- 229910000679 solder Inorganic materials 0.000 description 15
- 230000007547 defect Effects 0.000 description 9
- 230000004907 flux Effects 0.000 description 8
- 239000013078 crystal Substances 0.000 description 4
- 230000005499 meniscus Effects 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 4
- 150000004706 metal oxides Chemical class 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 230000008646 thermal stress Effects 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 238000009529 body temperature measurement Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 244000025254 Cannabis sativa Species 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003985 ceramic capacitor Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000004590 computer program Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K1/00—Soldering, e.g. brazing, or unsoldering
- B23K1/012—Soldering with the use of hot gas
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K3/00—Tools, devices, or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
- B23K3/04—Heating appliances
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K3/00—Tools, devices, or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
- B23K3/08—Auxiliary devices therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/36—Electric or electronic devices
- B23K2101/42—Printed circuits
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Electric Connection Of Electric Components To Printed Circuits (AREA)
Abstract
The invention is applicable to the technical field of control, and provides a precise control method for SMT reflow soldering furnace temperature, which comprises the following steps: determining a standard temperature curve of the selected standard PCB reflow soldering, and decomposing the standard temperature curve into control parameters of a preheating zone, a constant temperature zone, a reflow zone and a cooling zone according to a reflow soldering process; after a piece to be welded is placed in a reflow soldering furnace, the temperature in the furnace is increased to a first active temperature according to a first heating rate, and the control parameters of the preheating zone are followed by the first heating rate in real time; maintaining the temperature in the furnace between the first active temperature and the second active temperature for 60-120 seconds; the second active temperature is greater than the first active temperature; raising the temperature in the furnace to the highest temperature range and maintaining for 45-75 seconds; according to the invention, the standard temperature curve is measured according to the preheating zone, the constant temperature zone, the reflow zone and the cooling zone, and reflow soldering of the to-be-soldered piece is accurately controlled according to the measured data, so that the soldering quality is high.
Description
Technical Field
The invention belongs to the technical field of control, and particularly relates to a precise control method for an SMT reflow soldering furnace temperature.
Background
The basic flow of the SMT process comprises: solder paste printing, part mounting, reflow soldering, cleaning, AOI optical detection, maintenance and board separation.
Wherein, the SMT paster (Surface Mount Technology, electronic circuit surface assembling technique; surface mounting for short) refers to the short of series of process flows for processing on the basis of PCB (printed circuit board); in the reflow soldering of SMT (surface mount technology) patch production, too low temperature can lead to unmelted cold soldering of soldering tin, and too high temperature can lead to baking damage of electronic elements on a PCB (printed Circuit Board), so that the temperature of a precise reflow soldering furnace is a key for ensuring the whole soldering quality; improvements are needed.
Disclosure of Invention
The embodiment of the invention aims to provide a precise control method for the temperature of an SMT reflow soldering furnace, which can solve the problems that the temperature is too low and the soldering is easy to be low in the reflow soldering in the prior art.
The embodiment of the invention is realized in such a way that the accurate control method of the SMT reflow soldering furnace temperature comprises the following steps:
determining a standard temperature curve of the selected standard PCB reflow soldering, and decomposing the standard temperature curve into control parameters of a preheating zone, a constant temperature zone, a reflow zone and a cooling zone according to a reflow soldering process;
after a piece to be welded is placed in a reflow soldering furnace, the temperature in the furnace is increased to a first active temperature according to a first heating rate, and the control parameters of the preheating zone are followed by the first heating rate in real time;
maintaining the temperature in the furnace between the first active temperature and the second active temperature for 60-120 seconds; the second active temperature is greater than the first active temperature;
raising the temperature in the furnace to the highest temperature range and maintaining for 45-75 seconds; the highest temperature in the highest temperature range is controlled between 235 and 250 ℃;
and performing furnace cooling, and controlling the numerical value of the cooling rate during cooling to be not more than the maximum value of the first heating rate.
In a further aspect of the present invention, the step of determining the standard temperature profile of the selected standard PCB board reflow soldering may be specifically implemented by a simulation determination, a physical determination, or both the simulation determination and the physical determination.
As a further scheme of the invention, the standard temperature curve of the selected standard PCB reflow soldering is measured through simulation, and the method specifically comprises the following steps:
selecting a standard PCB, setting a temperature measuring probe, and connecting the temperature measuring probe with a thermometer;
placing a standard PCB provided with a temperature measuring probe in a reflow soldering furnace, and simulating the furnace passing action of normal production to test the temperature in the furnace;
after the test is finished, reading temperature data acquired by the temperature detector through the temperature probe, and generating a furnace temperature curve; obtaining the standard temperature curve.
As a further scheme of the invention, the number of times of the simulation measurement is more than two, and further more than two furnace temperature curves are obtained;
fitting all furnace temperature curves to obtain the standard temperature curve.
As a further aspect of the present invention, the method further includes:
after decomposing control parameters of the preheating zone, the constant temperature zone, the reflux zone and the cooling zone, deriving the control parameters of the preheating zone, the constant temperature zone, the reflux zone and the cooling zone to obtain a preheating control component, a constant temperature control component, a reflux control component and a cooling control component;
after placing a piece to be welded into a reflow soldering furnace, acquiring the temperature in the furnace in real time;
and controlling the temperature in the furnace according to the preheating control component, the constant temperature control component, the reflux control component or the cooling control component at corresponding time on time sequence, so as to realize the reflow soldering of the parts to be soldered.
As a further aspect of the present invention, the step of controlling the first heating rate in real time follows the control parameters of the preheating zone specifically includes:
deriving control parameters of the preheating zone to obtain a preheating control component;
and acquiring a first heating rate in real time, differencing the first heating rate with a preheating control component at a corresponding moment, and regulating the temperature in the furnace according to the acquired difference value to enable the difference value to approach zero so as to enable the first heating rate to follow the control parameters of the preheating zone.
As a further scheme of the invention, in the process of adjusting the first active temperature to the second active temperature, the temperature change rate at each moment is recorded as a second heating rate, and the second heating rate is adjusted in real time according to the control parameters of the constant temperature zone.
As a further scheme of the invention, the value range of the second active temperature is 150-200 ℃.
The precise control method of the SMT reflow soldering oven temperature according to claim 1, wherein the temperature in the oven is raised to a highest temperature range and maintained for 45-75 seconds; the method specifically comprises the steps of controlling the highest temperature in the highest temperature range to 235-250 ℃, wherein the method specifically comprises the following steps of:
according to the control parameters of the reflux zone, the temperature in the furnace is increased to 220 ℃ from the second active temperature; then, the temperature in the furnace is controlled to be increased to be more than 235 ℃ and less than 250 ℃; maintaining the temperature in the furnace at 220 ℃ for 45-75 seconds.
As a further aspect of the present invention, the step of performing furnace cooling specifically includes:
controlling the temperature in the furnace to be reduced at a constant speed according to a numerical value not greater than the first heating rate;
or the temperature in the variable speed control furnace is reduced, and the value at any time during the variable speed is not more than the maximum value of the first temperature rising rate.
As a further scheme of the invention, the cooling rate for cooling the furnace is as follows: 1-5 ℃/s.
As a further aspect of the present invention, the range of the first heating rate is: 1-5 ℃/s.
As a further scheme of the invention, the optimal value of the first heating rate is 3 ℃/s.
Compared with the prior art, the accurate control method for the SMT reflow soldering furnace temperature provided by the embodiment of the invention has the following beneficial effects: according to preheating zone, constant temperature zone, backward flow district and cooling zone, survey standard temperature curve to according to the reflow soldering of the accurate control piece that waits to weld of data that determines, if so, wait to weld when the piece is PCBA (printed circuit board), can be in constant temperature zone: enabling the temperature of all elements on the PCBA to be consistent, volatilizing volatile substances in the solder paste, enabling the soldering flux in the solder paste to start working and performing chemical reaction with a metal oxide layer of a welding part to remove the oxide layer so as to form a clean welding surface; in the reflux zone: a critical welding area, which enables solder particles to start to melt, starts a 'rush' process of liquefying and sucking tin on the surface, covers all possible surfaces, and starts to form a tin welding spot; the damage to the PCB and components caused by the overhigh peak temperature or overlong reflow time is avoided; and, the peak temperature is too low or the reflow time is too short, the wettability of the soldering tin may be deteriorated, so that a high-quality welding spot cannot be formed, and defects such as cold welding and cold welding are easily caused; in the cooling zone: the welding spot is cooled rapidly and solidified, the welding spot is cooled rapidly, the welding flux crystal lattice is thinned, the bonding strength is improved, the welding spot is bright, and the surface is continuously 'in a meniscus'; the defects of damage to components, cracking of welding spots and the like caused by overlarge thermal stress can be avoided due to the fact that the cooling rate is too high.
Drawings
Fig. 1 is a flowchart of a method for precisely controlling the temperature of an SMT reflow soldering furnace according to the present embodiment;
FIG. 2 is a flow chart of the standard temperature curve (i.e., standard furnace temperature curve) in the present embodiment;
fig. 3 is a graph of standard furnace temperature in this example (where the horizontal axis represents time and the vertical axis represents temperature).
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Fig. 1 is a flowchart of a method for precisely controlling the temperature of an SMT reflow soldering furnace according to an embodiment of the present invention, which specifically includes the following steps S101 to S109:
s101, measuring a standard temperature curve of the selected standard PCB reflow soldering, wherein the standard temperature curve is a standard furnace temperature curve shown in FIG. 3; decomposing the standard temperature curve into control parameters of a preheating zone, a constant temperature zone, a reflow zone and a cooling zone at least according to a reflow soldering process;
in this step, the step of determining the standard temperature curve of the selected standard PCB reflow soldering may be specifically implemented by analog determination, physical determination, or by both analog determination and physical determination.
In one example of this embodiment, the standard furnace temperature curve may be measured in advance, or may be measured after the part to be soldered is selected, and the standard PCB board is selected according to the part to be soldered.
In one example of the present embodiment, the standard temperature curve is not limited to four process zones, i.e., the preheating zone, the constant temperature zone, the reflow zone, and the cooling zone, which are control parameters of the reflow soldering process, but may be divided into other modes, which will not be described in detail herein.
As shown in fig. 2, the standard temperature curve of the selected standard PCB reflow soldering is determined by simulation, and specifically includes:
s202, selecting a standard PCB, setting a temperature measurement probe, and connecting the temperature measurement probe with a thermometer;
manufacturing a temperature measuring plate by PCBA of the standard PCB, installing a temperature measuring probe at a key component position, connecting the other end of the temperature measuring probe with a temperature measuring instrument, wherein the temperature measuring probe and the temperature measuring instrument are mature devices which are seen in the market and are not described in detail herein;
s204, placing the standard PCB provided with the temperature measuring probe into a reflow soldering furnace, and simulating the furnace passing action of normal production to test the temperature in the furnace; the furnace passing actions of normal production include preheating, constant temperature, reflux, cooling and the like.
S206, reading temperature data acquired by the thermometer through the temperature probe after the test is completed, and generating a furnace temperature curve; obtaining the standard temperature curve.
S103, after the piece to be welded is placed in a reflow soldering furnace, the temperature in the furnace is increased to a first active temperature according to a first heating rate, and the first heating rate is controlled in real time to follow the control parameters of the preheating zone;
in this step, the first heating rate follows the control parameters of the preheating zone, and generally, the first heating rate is adjusted and controlled according to the curvature change of the curve represented by the control parameters of the preheating zone.
S105, maintaining the temperature in the furnace between the first active temperature and the second active temperature for 60-120 seconds; the second active temperature is greater than the first active temperature;
for example: in fig. 3, the first active temperature is 150 ℃, the second active temperature is 200 ℃, and the second active temperature is greater than the first active temperature; obviously, for the subsequent process temperature rise, the temperature can be kept in a constant temperature zone for 60-120 seconds, but not more than 200 ℃; in addition, the temperature can also be kept constant at 150, 175, 190 or 200 ℃ in a constant temperature zone for 60-120 seconds;
the temperature maintained can be different according to the different plates of the to-be-welded piece and can be 60, 70, 80, 100, 110 or 120 seconds, and particularly can be flexibly selected according to the actual implementation;
s107, raising the temperature in the furnace to a highest temperature range and maintaining for 45-75 seconds; the maximum temperature in the maximum temperature range is controlled to 235-250deg.C, such as 220-235deg.C, 250deg.C, 235 deg.C, 240 deg.C, 245 deg.C or 250deg.C; while the maintained temperature can be controlled in the range of 45-75 seconds depending on the actual conditions;
and S109, performing furnace cooling, and controlling the numerical value of the cooling rate in cooling to be not more than the maximum value of the first heating rate. And cooling in a furnace to obtain a finished PCBA product subjected to reflow soldering.
In one example of this embodiment, the preheating zone (a→b in the figure) can be seen in the standard furnace temperature curve shown in fig. 3: this temperature zone is primarily to raise the temperature of the PCBA from ambient temperature to a desired active temperature, i.e., a first active temperature, in one example specifically 150 ℃; the temperature zone is mainly used for controlling the temperature rising rate, namely the first temperature rising rate, and is generally controlled to be 1-5 ℃/s, and the optimal temperature rising rate is 3 ℃/s, because the temperature rising is too fast, certain defects, such as tin balls generated by tin paste splashing, cracks generated by a ceramic capacitor and the like, are easily caused, and the temperature rising is too slow, so that the temperature of the tin paste is excessively sensed, and the time is insufficient for enabling the PCBA to reach the active temperature.
Constant temperature zone (b→c in the figure): the temperature zone is also called an active zone, and mainly aims to enable the temperature of all elements on the PCBA to be consistent, volatilize volatile substances in the solder paste, start working of the soldering flux in the solder paste and the metal oxide layer of the welding part to chemically react to remove the oxide layer and form a clean welding surface, and the temperature change of the temperature zone is not excessively large and is generally 150-200 ℃ (namely the first active temperature to the second active temperature), and the time is controlled to be 60-120 seconds.
Reflux zone (c→d in the figure): the temperature zone is a key welding zone, after entering the temperature zone, solder particles start to melt, and start to liquefy and the process of 'lamp grass' of surface tin absorption, cover all possible surfaces, and start to form tin welding spots; the peak temperature of the temperature zone, namely the highest temperature, is controlled to be 235-250 ℃, and the reflux time (more than 220 ℃) is controlled to be 45-75 seconds; if the peak temperature is too high or the reflow time is too long, damage to PCBA and components may be caused; if the peak temperature is too low or the reflow time is too short, the wettability of the solder may be deteriorated, and high quality solder joints may not be formed, and defects such as cold soldering and cold soldering may be easily caused.
Cooling zone (d→e in the figure): after the PCBA enters the cooling area, the welding spot is rapidly cooled and the soldering tin is solidified, the welding spot is rapidly cooled to refine the crystal lattice of the soldering flux, the bonding strength is improved, the welding spot is bright, the surface is continuously 'in a meniscus', the cooling rate in the cooling area is controlled within 5 ℃/s, if the cooling rate is too fast, the damage of components and parts can be caused by bearing excessive thermal stress, and the welding spot has defects such as cracks and the like.
In this embodiment, according to the method for precisely controlling the temperature of the SMT reflow soldering furnace, a standard temperature curve is measured according to a preheating zone, a constant temperature zone, a reflow zone and a cooling zone, and reflow soldering of a piece to be soldered is precisely controlled according to measured data, so that when the piece to be soldered is a PCBA (printed circuit board), the standard temperature curve can be measured in the constant temperature zone: enabling the temperature of all elements on the PCBA to be consistent, volatilizing volatile substances in the solder paste, enabling the soldering flux in the solder paste to start working and performing chemical reaction with a metal oxide layer of a welding part to remove the oxide layer so as to form a clean welding surface; in the reflux zone: a critical welding area, which enables solder particles to start to melt, starts a 'rush' process of liquefying and sucking tin on the surface, covers all possible surfaces, and starts to form a tin welding spot; the damage to PCBA and components caused by the overhigh peak temperature or overlong reflow time is avoided; and, the peak temperature is too low or the reflow time is too short, the wettability of the soldering tin may be deteriorated, so that a high-quality welding spot cannot be formed, and defects such as cold welding and cold welding are easily caused; in the cooling zone: the welding spot is cooled rapidly and solidified, the welding spot is cooled rapidly, the welding flux crystal lattice is thinned, the bonding strength is improved, the welding spot is bright, and the surface is continuously 'in a meniscus'; the defects of damage to components, cracking of welding spots and the like caused by overlarge thermal stress can be avoided due to the fact that the cooling rate is too high.
It can be understood that the precise control method of the SMT reflow soldering furnace temperature can be applied to PCBA and can also be applied to the soldering of other circuit boards, when the precise control method is applied to other circuit boards, the mode of measuring the standard temperature curve is the same, and only fine adjustment of a preheating zone, a constant temperature zone, a reflow zone and a cooling zone is possible, so that the fine adjustment is easily selected by a person skilled in the art according to practice; the present embodiment is not limited thereto.
In one example of this embodiment, the number of times of the simulation measurement is two or more, and thus a furnace temperature curve of two or more times is obtained;
fitting all furnace temperature curves to obtain the standard temperature curve.
The fitting method is the prior art, for example: mean, variance, etc.;
in one example of this embodiment, a determination may be made of the finished PCBA that has been reflow soldered;
acquiring or calling actual furnace temperature data in the reflow soldering process, preparing an actual furnace temperature curve, and judging whether the PCBA finished product is qualified or not by comparing the standard furnace temperature curve and the actual furnace temperature curve; the difference between four-region data of the actually measured furnace temperature curve and standard data of the standard furnace temperature curve is compared to judge whether each item of data is in the range and is a qualified furnace temperature curve in the range, and the furnace temperature is required to be tested after the furnace temperature is correspondingly adjusted if the data is not in the range until the test is qualified. And PCBA finished products generated in the non-tested qualified state are inferior products.
In one example of this embodiment, the method further includes:
after decomposing control parameters of the preheating zone, the constant temperature zone, the reflux zone and the cooling zone, deriving the control parameters of the preheating zone, the constant temperature zone, the reflux zone and the cooling zone to obtain a preheating control component, a constant temperature control component, a reflux control component and a cooling control component;
after placing a piece to be welded into a reflow soldering furnace, acquiring the temperature in the furnace in real time;
and controlling the temperature in the furnace according to the preheating control component, the constant temperature control component, the reflux control component or the cooling control component at corresponding time on time sequence, so as to realize the reflow soldering of the parts to be soldered.
In one example of this embodiment, the step of controlling the first heating rate in real time follows the control parameter of the preheating zone specifically includes:
deriving control parameters of the preheating zone to obtain a preheating control component;
acquiring a first heating rate in real time, differencing the first heating rate with a preheating control component at a corresponding moment, and regulating the temperature in the furnace according to the acquired difference value to enable the difference value to approach zero so as to enable the first heating rate to follow the control parameter of the preheating zone; the PI closed-loop control mode has high timeliness and high control precision.
In one example of this embodiment, in the process of adjusting the first active temperature to the second active temperature, the temperature change rate at each moment is recorded as a second heating rate, and the second heating rate is adjusted in real time according to the control parameter of the constant temperature area.
The first active temperature is 150 ℃, and can be flexibly set according to the requirement;
in one example of this embodiment, the second activation temperature has a value in the range of 150-200 ℃.
For example: the second active temperature is 150, 165, 180 or 200 ℃;
in one example of this embodiment, the furnace temperature is raised to the highest temperature interval and maintained for 45-75 seconds; the method specifically comprises the steps of controlling the highest temperature in the highest temperature range to 235-250 ℃, wherein the method specifically comprises the following steps of:
according to the control parameters of the reflux zone, the temperature in the furnace is increased to 220 ℃ from the second active temperature; then, the temperature in the furnace is controlled to be increased to be more than 235 ℃ and less than 250 ℃; maintaining the temperature in the furnace at 220 ℃ for 45-75 seconds.
In one example of this embodiment, the step of performing furnace cooling specifically includes:
controlling the temperature in the furnace to be reduced at a constant speed according to a numerical value not greater than the first heating rate;
or the temperature in the variable speed control furnace is reduced, and the value at any time during the variable speed is not more than the maximum value of the first temperature rising rate.
In one example of this embodiment, the cooling rate at which furnace cooling is performed is: 1-5 ℃/s.
Preferably, the cooling rate for furnace cooling is 3 ℃/s.
In one example of the present embodiment, the first temperature rising rate ranges from: 1-5 ℃/s.
In one example of this embodiment, the optimal value of the first heating rate is 3 ℃/s.
In another embodiment, there is provided a computer device including a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform steps S101 to S109 of the method as described above;
s101, measuring a standard temperature curve of reflow soldering of a selected standard PCB, and decomposing control parameters of a preheating zone, a constant temperature zone, a reflow zone and a cooling zone according to the standard temperature curve by a reflow soldering process;
s103, after the piece to be welded is placed in a reflow soldering furnace, the temperature in the furnace is increased to a first active temperature according to a first heating rate, and the first heating rate is controlled in real time to follow the control parameters of the preheating zone;
s105, maintaining the temperature in the furnace between the first active temperature and the second active temperature for 60-120 seconds; the second active temperature is greater than the first active temperature;
s107, raising the temperature in the furnace to a highest temperature range and maintaining for 45-75 seconds; the highest temperature in the highest temperature range is controlled between 235 and 250 ℃;
and S109, performing furnace cooling, and controlling the numerical value of the cooling rate in cooling to be not more than the maximum value of the first heating rate.
Above, according to the method for precisely controlling the temperature of the SMT reflow soldering furnace provided in the present embodiment, the standard temperature curve is measured according to the preheating zone, the constant temperature zone, the reflow zone and the cooling zone, and the reflow soldering of the workpiece to be soldered is precisely controlled according to the measured data, so that the temperature of the workpiece to be soldered can be controlled in the constant temperature zone: enabling the temperature of all elements on the PCBA to be consistent, volatilizing volatile substances in the solder paste, enabling the soldering flux in the solder paste to start working and performing chemical reaction with a metal oxide layer of a welding part to remove the oxide layer so as to form a clean welding surface; in the reflux zone: a critical welding area, which enables solder particles to start to melt, starts a 'rush' process of liquefying and sucking tin on the surface, covers all possible surfaces, and starts to form a tin welding spot; the damage to the PCB and components caused by the overhigh peak temperature or overlong reflow time is avoided; and, the peak temperature is too low or the reflow time is too short, the wettability of the soldering tin may be deteriorated, so that a high-quality welding spot cannot be formed, and defects such as cold welding and cold welding are easily caused; in the cooling zone: the welding spot is cooled rapidly and solidified, the welding spot is cooled rapidly, the welding flux crystal lattice is thinned, the bonding strength is improved, the welding spot is bright, and the surface is continuously 'in a meniscus'; the defects of damage to components, cracking of welding spots and the like caused by overlarge thermal stress can be avoided due to the fact that the cooling rate is too high.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (13)
1. The accurate control method of the SMT reflow soldering furnace temperature is characterized by comprising the following steps of:
determining a standard temperature curve of the selected standard PCB reflow soldering, and decomposing the standard temperature curve into control parameters of a preheating zone, a constant temperature zone, a reflow zone and a cooling zone according to a reflow soldering process;
after a piece to be welded is placed in a reflow soldering furnace, the temperature in the furnace is increased to a first active temperature according to a first heating rate, and the control parameters of the preheating zone are followed by the first heating rate in real time;
maintaining the temperature in the furnace between the first active temperature and the second active temperature for 60-120 seconds; the second active temperature is greater than the first active temperature;
raising the temperature in the furnace to the highest temperature range and maintaining for 45-75 seconds; the highest temperature in the highest temperature range is controlled between 235 and 250 ℃;
and performing furnace cooling, and controlling the numerical value of the cooling rate during cooling to be not more than the maximum value of the first heating rate.
2. The method of claim 1, wherein the step of determining the standard temperature profile of the selected standard PCB reflow soldering is performed by analog determination, physical determination, or both analog and physical determination.
3. The precise control method of the SMT reflow soldering oven temperature according to claim 2, wherein the standard temperature profile of the selected standard PCB board reflow soldering is determined by simulation, specifically comprising:
selecting a standard PCB, setting a temperature measuring probe, and connecting the temperature measuring probe with a thermometer;
placing a standard PCB provided with a temperature measuring probe in a reflow soldering furnace, and simulating the furnace passing action of normal production to test the temperature in the furnace;
after the test is finished, reading temperature data acquired by the temperature detector through the temperature probe, and generating a furnace temperature curve; obtaining the standard temperature curve.
4. The precise control method of the SMT reflow soldering furnace temperature according to claim 3, wherein the simulation measurement is performed twice or more, and further furnace temperature curves of two or more times are obtained;
fitting all furnace temperature curves to obtain the standard temperature curve.
5. The precise control method of SMT reflow soldering oven temperature of claim 1, further comprising:
after decomposing control parameters of the preheating zone, the constant temperature zone, the reflux zone and the cooling zone, deriving the control parameters of the preheating zone, the constant temperature zone, the reflux zone and the cooling zone to obtain a preheating control component, a constant temperature control component, a reflux control component and a cooling control component;
after placing a piece to be welded into a reflow soldering furnace, acquiring the temperature in the furnace in real time;
and controlling the temperature in the furnace according to the preheating control component, the constant temperature control component, the reflux control component or the cooling control component at corresponding time on time sequence, so as to realize the reflow soldering of the parts to be soldered.
6. The method of claim 1, wherein the step of controlling the first heating rate in real time follows the control parameters of the preheating zone, specifically comprises:
deriving control parameters of the preheating zone to obtain a preheating control component;
and acquiring a first heating rate in real time, differencing the first heating rate with a preheating control component at a corresponding moment, and regulating the temperature in the furnace according to the acquired difference value to enable the difference value to approach zero so as to enable the first heating rate to follow the control parameters of the preheating zone.
7. The precise control method of the temperature of the SMT reflow soldering oven according to claim 1, wherein in the process of adjusting the first active temperature to the second active temperature, the temperature change rate at each moment is recorded as a second heating rate, and the second heating rate is adjusted in real time according to the control parameter of the constant temperature area.
8. The precise control method of the SMT reflow soldering oven temperature according to claim 1, wherein the value range of said second active temperature is 150-200 ℃.
9. The precise control method of the SMT reflow soldering oven temperature according to claim 1, wherein the temperature in the oven is raised to a highest temperature range and maintained for 45-75 seconds; the method specifically comprises the steps of controlling the highest temperature in the highest temperature range to 235-250 ℃, wherein the method specifically comprises the following steps of:
according to the control parameters of the reflux zone, the temperature in the furnace is increased to 220 ℃ from the second active temperature; then, the temperature in the furnace is controlled to be increased to be more than 235 ℃ and less than 250 ℃; maintaining the temperature in the furnace at 220 ℃ for 45-75 seconds.
10. The method for precisely controlling the furnace temperature of the SMT reflow soldering of claim 1, wherein said step of performing furnace cooling specifically comprises:
controlling the temperature in the furnace to be reduced at a constant speed according to a numerical value not greater than the first heating rate;
or the temperature in the variable speed control furnace is reduced, and the value at any time during the variable speed is not more than the maximum value of the first temperature rising rate.
11. The precise control method of the SMT reflow soldering oven temperature according to claim 1, wherein the cooling rate for the oven cooling is: 1-5 ℃/s.
12. The precise control method of the SMT reflow soldering oven temperature of claim 1, wherein the range of the first heating rate is: 1-5 ℃/s.
13. The precise control method of the SMT reflow soldering oven temperature of claim 12, wherein the optimal value of the first heating rate is 3 ℃/s.
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| CN202311622284.3A CN117483893A (en) | 2023-11-30 | 2023-11-30 | Accurate control method for SMT reflow soldering furnace temperature |
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| CN202311622284.3A CN117483893A (en) | 2023-11-30 | 2023-11-30 | Accurate control method for SMT reflow soldering furnace temperature |
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