JP2848960B2 - Soldering method of printed wiring board under low pressure - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for brazing an electronic component to a printed wiring board or other components to be joined by brazing.

[Background Art] Pluggable / fittable or surface mountable electronic components to be finally soldered (= Surface Mounted Devices)
The use of electronic components configured in the form of printed wiring boards with SMDs) is ever increasing. In order to produce this electronic component, it is necessary to equip a suitably prepared printed wiring board with the corresponding components, which may be glued or glued before the soldering process. The printed wiring board and the component must be fixedly and conductively connected to one another by means of a soldering process, which are pre-positioned by the solder paste. Today, the soldering process is carried out in a first conventional manner by means of a soldering brazing apparatus, in which the solder is applied to the corresponding area by means of one or more soldering waves which contact the printed wiring board from below. The corresponding components are thus soldered together. Secondly, in the case of a system in which a solder paste, a solder formation or a solder deposit is adhered to the component, the solder component of the solder paste or the solder formation simply needs to be remelted ( Reflow soldering method = Refl
owloeten).

In either case, fluxing agents must be used to obtain good quality brazed joints. In the case of brazing soldering, the fluxing agent is applied to the actual brazing process rain, or the brazing paste or solder composition used contains both brazing and fluxing agents. The fluxing agent contributes, inter alia, to the brazing process, as long as it impairs the brazing and destroys the metal oxide phase on the workpiece surface and prevents the oxidation of the relevant metals during the brazing process. Furthermore, the surface tension of the liquefied solder is also avoided. In essence, fluxing agents are multifunctional, so their composition is made up of a number of substances. However, after the soldering process, residues of the fluxing agent remain on the printed circuit board surface, causing adverse consequences. Examples of this disadvantageous result include premature erosion of the insulation resistance between the conductive paths located on the printed wiring board surface or the conductive paths. Therefore, it is necessary to remove the residue of the fluxing agent. This removal is done after the soldering process as in the surroundings
It is obtained by performing a cleaning process on a printed wiring board by FCKW or CKW. However, the use of the pollutants mentioned here and, as is well known, polluting the environment must now be minimized (from the point of view of the FCKW-ozone problem) or totally avoided.

In a recent approach, the need for a fluxing agent is preceded by a pretreatment step of the substrate with a low-pressure plasma prior to the soldering step of the substrate, with the application of microwaves and / or under glow discharge. It is at least reduced by generating a plasma from the process gas (see DE 3936955). However, following the pre-treatment step, the brazing process is again in air at standard pressure,
Alternatively, it is carried out by locally supplying the protective gas very locally. In short, in this case, during the dwell between the pretreatment point and the soldering point, there is no barrier to oxygen, so that oxide deposition and / or oxide formation occurs again at the soldered part, which results in a low soldering performance. This has the disadvantage of having a negative effect on For this reason, it is generally not possible to completely abandon the use of fluxing agents or auxiliaries of the same effect in the known processes.

Furthermore, a fluxing-free soldering method in which a solder is placed on the surface of the workpiece before cooling, that is, before mounting, and then cooled to form a surface oxide layer, is disclosed in U.S. Pat. No. 4,921,157. Following this brazing, the actual brazing process, which attempts to form a brazing joint to the corresponding surface, takes place for the first time. In that case, in order to solder the two surfaces to be joined, the existing solder must be reliquefied (reflowed). In short, the invention described in the above-mentioned U.S. patent is based in particular on the principle of reflow, in which case it is well known that the reliquefaction of the already existing solder has particular problems. As a solution to this problem, the above-cited U.S. Pat. No. 6,077,045 discloses a method in which a fluorine-containing plasma is applied to an existing brazing bead (usually attacked by a fluxing agent) prior to and partially during reflow. It has been proposed to break the layer and then form the desired joint again at ambient pressure or under the action of a plasma. In essence, plasma pretreatment is still applied to assist the brazing process, but reflow brazing has different problems than solder brazing.

DISCLOSURE OF THE INVENTION It is therefore an object of the present invention to provide a high-quality soldering of printed circuit boards on which the device has been implemented, with a low error rate.

Means for solving the above-mentioned problems in the method according to the present invention include a supply step of supplying an electronic component to a printed wiring board for surface mounting, a preheating step preceding a soldering step, and a solder bath. A soldering step of transporting said printed circuit board along one or more flowing soldering surfaces of liquid phase soldering generated from said soldering and performing a soldering operation by means of one or more soldering waves during said transporting; A method of brazing an electronic component to a printed wiring board according to a brazing process, which comprises a cooling stage followed by a brazing stage to cure the soldering process. Under the action of the plasma of the process gas.

In an advantageous embodiment, the preceding, intermediate or subsequent processing stages, such as for example the heating and cooling stages, are implemented under a low pressure equal to that of the brazing process, in which case no more than 100 mbar, In particular, operation is carried out under low pressures of 0.5 to 20 mbar.

In an advantageous embodiment, the components to be joined by brazing are pretreated during the preheating stage by a plasma action generated in the pretreatment zone or by a plasma action reaching into the pretreatment zone, To form the atmosphere of the pretreatment zone, the same process gas used to create the brazing atmosphere is used. However, in other applications, it is advantageous for the atmosphere during the preheating stage to be different from the gas atmosphere during the brazing process.

It is particularly advantageous that at least a reducing and oxidizing process gas is selected as the plasma. In this way, both oxides and other impurities, such as greasy residues, are effectively removed or kept away during processing of the workpiece.

0.5-10 volume% of oxygen as a process gas in the present invention, is particularly advantageous to use a 80 to 20 volume% of hydrogen and 20 to 80 volume percent CF _4, N ₂ or a mixed gas consists Ar is there.

Although known in principle, the invention advantageously generates a plasma from the process gas mixture by the action of microwaves, radio frequencies and / or glow discharges.

In a particularly advantageous embodiment of the invention, the plasma generation takes place directly around the brazing process, that is to say at the brazing site, so that in particular the brazing takes place in a strong plasma atmosphere. By this measure, further quality advantages are obtained. In a particularly advantageous embodiment of the invention, in the case of brazing, the bath is connected as a cathode of a glow discharge by means of a brazing and a plasma is generated directly there.

In many cases, the generation of a plasma at the brazing site also offers the possibility that it is not necessary to generate another plasma independently at another site. This is because the effect of the plasma generated at the brazing site also reaches into the brazing equipment area located in front of the brazing site, so that a sufficient brazing preparation can be obtained at said other site. But it is already available.

Further advantageous embodiments of the soldering method according to the invention are evident from the dependent claims of the claims.

The above-mentioned object of the present invention is also achieved by a soldering station and a plurality of other processing stations, i.e., a continuous soldering apparatus having a preheating station and a cooling zone or an advance zone. , An equipment room surrounding the brazing station and other processing stations and hermetically sealed, and a procedure for generating a low pressure in the equipment room, and a part for generating a solder wave In which the brazing bath is connected as a cathode to an anode arranged above the brazing bath,
Alternatively, a device for forming a low-pressure atmosphere in a plasma state by arranging a microwave transmitter or an HF oscillator in the region of the solder wave is provided.

If the gas atmosphere in the different installation areas is different, between the individual processing stations, in particular between the preheating zone and the brazing zone, gas flow baffle members are incorporated. Advantageously.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view, partially in section, of a soldering brazing apparatus according to the present invention.

FIG. 2 is a schematic sectional view of the continuous reflow soldering equipment according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described in detail with reference to the drawings.

The soldering equipment shown in FIG. 1 comprises an inlet airlock gate 1 and an equipment room 6 with an inlet and pre-treatment station 2, a transfer station 3, a soldering soldering station 4 and an exit passage 5, and This is a soldering type brazing equipment of the type equipped with an outlet airlock gate 7.

The operation process of the illustrated soldering maintenance is as follows. That is, first, the stack unit 13 on which the printed wiring board 10 is loaded is introduced into the entrance airlock gate 1. To this end, the outboard lock gate slider 11 is first opened, so that the inlet lock chamber is placed under ambient atmospheric pressure. Pump switchable after closing the lock gate slider 11
Air is sucked out of the inlet airlock gate 1 by 16. After a suitable time, that is, when the air has been sufficiently exhausted from the inlet lock chamber, the inlet lock chamber is filled with a process gas or an inert gas, for example nitrogen. This sucking
The cooling cycle can optionally be performed multiple times for reasons of atmospheric purity. Finally, the pump is evacuated, and this evacuation is carried out in the equipment room 6 of the brazing equipment, that is, at the inlet / pre-treatment station 2 and the delivery station 3
And until a pressure level is established in the inlet airlock gate 1 such as is present in the soldering station and also in the exit passage 5. In this example, a pressure level of approximately 1-2 mbar is maintained in the installation room 6 by means of a main pump 18 located below the installation room 6 and a suitable supply of process gas. This pressure level must ultimately also be established in the lock chamber of the inlet airlock gate 1.

When the pressure equilibrium between the inlet air lock gate 1 and the equipment room 6 is completely achieved, the inner lock gate slider
12 is opened, and the printed wiring boards 10 are transferred one by one from the stack unit 13 into the entrance / pre-processing station 2. For this transfer, an extruding device 14 arranged in the inlet airlock gate 1 is used.
The printed wiring board is sent out from the section of the stack unit 13, and the printed wiring board is carried on a belt conveyor 22 whose height and running speed are appropriately adjusted in each case. The initial supply of the process gas into the equipment room takes place via a nozzle assembly 21 arranged above the equipment room 6 behind the inward lock gate slider 12. By means of the nozzle assembly, a suitable amount of process gas (the amount of process gas is substantially related to the set exhaust power of the menpump 18 and the desired installation pressure) is introduced into the brazing facility (in the illustrated installation, , As a whole, about
0.2 to 0.5 Nm ³ / h, generally 0.1 to 2.0 Nm ³ / h of process gas must be supplied). A microwave transmitter 23 is disposed near the nozzle assembly 21 in the entrance / pretreatment station 2. The microwave transmitter is used to generate a plasma from a process gas, that is, to make a gas mixture containing reactive groups and ions from the process gas. For this reason, microwave excitation requires power 10
The operation is performed at 0 to 1000 watts and a frequency of about 2.5 GHz. In this way, at the inlet and pretreatment station 2, the effective gas from a process gas consisting of preferably 2-8% by volume of oxygen 40-60% by volume of hydrogen and 30-55% by volume of tetrafluorocarbon (CF ₄ ) Plasma is generated. Since this plasma obtained from the gas mixture has an oxidizing action and a reducing action, as a result, after a sufficient operating time, the oleaginous substance and the oily substance are always present from the printed wiring board to be treated. Whereas, the metal oxide layer which interferes with the brazing process will both be removed behind the entrance to the brazing facility. In the normal case, the staying time required to make the printed wiring board stay in the plasma working area is 0.5 to 3.0 minutes. This working time is easily maintained in the illustrated soldering installation by controlling the transport speed in the inlet and pretreatment station 2.

Furthermore, it should be noted with respect to the soldering equipment shown that after the printed circuit board 10 has exited the entry and pre-treatment station 2 and has been transferred to the transfer station 3 by the belt conveyor 31, the printed circuit board 10 is still in contact with the plasma. The operation area is not completely removed, and the plasma generated at the entrance / pretreatment station 2 is also affected within the area of the transfer station 3. In the present invention, unlike the known process, the printed wiring board is under the action of a process gas or a partial plasma gas under low pressure and at a higher pressure, possibly an impure atmosphere. It will not be exposed again. In short, the situation in which oxygen is added again or oxidation occurs is basically avoided, and a component preparation state suitable for brazing is maintained.

The printed wiring board at the end of the delivery station 3
It is handed over to a free-hanging transport type transport device 44 having a plurality of support elements 46. For this delivery, the conveyor speed of the belt conveyor 31 and the suspension conveyor 44 are synchronized. The lifting and conveying device 44 now conveys the printed wiring board 10 at a suitable ascending angle to two solder waves 40 and 42 (double soldering), and transports it over the soldering wave. It is preheated via a preheating device 28, which is an infrared irradiator. The soldering is carried out by the two soldering waves 40, 42, in which case the solder does not come into contact with the printed wiring area pretreated with the anti-adhesive. In the brazing process itself, low pressure conditions and process gas atmospheres result in a mobile, slightly wettable braze that does not require a flux additive. In this case, it is advantageous to arrange another process gas supply 34 adjacent to the soldering waves 40,42.

In a particularly advantageous embodiment of the invention, a brazing bath 48 together with two brazings 40, 42 is provided with an anode,
It is polarized as a cathode to 49, so that a glow discharge plasma generation takes place directly above the brazing bath and the brazing waves, resulting in a special activation and an additional advantageous effect on the brazing process. Occurs. In this way, a remarkably high quality brazed joint is obtained and the incidence of brazing errors is particularly low. In an advantageous embodiment of the invention, the plasma generation, together with the brazing, is combined with a suitably arranged microwave transmitter or
Can be obtained by HF oscillator.

In many cases, for example, if, in principle, the printed circuit board is not contaminated and / or oxidized to a standard scale,
The brazing equipment according to the invention can also be operated without independent plasma formation at the inlet and pretreatment station 2.
This is because the plasma generated at the soldering site already sufficiently pre-treats the printed wiring board during the feeding of the printed wiring board to the soldering wave, while the plasma action remains unchanged even in the soldering operation. Is maintained. In this case, and as is generally the case, it goes without saying that the action of the plasma is not limited to the range of direct generation of the plasma.

After passing through the soldering station 4, the printed circuit board just soldered enters the exit passage 5 of the soldering equipment. The exit path has a transport device 51 by means of which the printed circuit board is taken off and transferred from the brazing station 4. The exit passage 5 leads to an outlet airlock gate 7 with an associated lockgate slider. The printed wiring board is fed to the outlet airlock gate by the transfer device 51 as follows. In other words, for example, two printed wiring boards are
Immediately after being transferred to the transfer device 51, both printed wiring boards are transferred at high speed into the outlet airlock gate 7 by the time the next printed wiring board arrives. The time required for the lock-type discharge process is obtained. For the pneumatic locking process, the output airlock gate 7 is filled with air or, for example, nitrogen until it reaches the surroundings, and then the lockgate slider of the outlet airlock gate is opened. The printed wiring board that has advanced from the exit airlock gate 7 has been completely processed. That is, based on a processing method that does not use a flux agent,
This is because there is no need for post-purification work conventionally used conventionally. Of course, the outlet airlock gate 7 must be evacuated again for the next airlocked discharge process.

FIG. 2 shows a continuous reflow soldering installation according to the invention, in which the printed circuit boards are passed one after the other through a soldering installation arranged on a conveyor 73. The printed circuit board is conveyed (in FIG. 2, the printed wiring board is omitted).

Continuous air reflow soldering equipment has an inlet airlock gate 71,
It has a preheating and pretreatment station 72, a brazing station 74 and an exit airlock gate 76. The depressurization of the main installation areas, in other words the preheating and pretreatment station 72, the brazing station 74 and the short exit zone 75 (both corresponding to the equipment room) is effected by means of a pump device (not shown). Through the inlet airlock gate 71,
The printed wiring boards to be processed are introduced individually or in small groups into the brazing equipment, in which case the charging of the printed wiring boards into the lock chamber takes place in accordance with the above-described stack unit scheme, Within a given charging cycle time (minimum of about 10 to 20 seconds). In order to transport the printed wiring board, a step-by-step feed is performed by the transport device 73 in accordance with the charging cycle, whereby the printed wiring board is transferred from one station to the next station,
And ultimately conveyed through the entire brazing facility.

At that time, the printed wiring board first moves from the entrance air lock gate 71 into the preheating / pretreatment station 72. Then, the supply of plasma gas and the first operation are performed.

In the example shown, plasma is formed from the process gas in the external plasma generator 80 and then supplied to the preheating / pretreatment station 72. As the process gas, for example, a mixed gas PG1 composed of 5% oxygen, 60% hydrogen, 35%, and carbon tetrafluoride (CF ₄ ) is used. Furthermore, in the area of the preheating and pretreatment station 72, the printed wiring board is preheated to about 150 ° C. by a suitable heating device. The transit time in the area and the processing time in the area are about 20 to 240 seconds. Following this, the printed wiring board is soldered to the station
Enter into 74. In this case, both the pretreatment zone and the brazing zone are at a pressure level of 5 mbar or less. However, in the brazing zone this example, the process gas mixture gas, such as is not supplied, mixed gas PG2 that contains nitrogen instead of CF ₄ rather is supplied. This is because, in the prechamber, ie behind the high-efficiency process gas by the preheating and pretreatment station 72, a brazing process gas containing an inert gas is sufficient, and again the plasma formation takes place externally. is there. At the brazing station 74, the brazing is finally released by a radiator arranged on the ceiling of the brazing station 74 (temperature about 210 ° C.). Thus, for example, the braze deposited in the form of a braze deposit, in other words, is melted on the brazed printed wiring board, which is dispensed and positioned in a suitable amount, and the components are brazed. In the illustrated soldering station, the soldering station is not airtight, but is separated from the upstream preheating and pretreatment station 72 and the downstream exit zone 75 by a partition wall 78, 79, but to block the gas flow. .
In this way it is possible to better maintain different atmospheres in different installation areas.

Due to the reflow operation at the soldering station 74, the cooling of the printed wiring locations has already started in the entry zone 75, in which case it is also possible for example to supply nitrogen. From the entry zone 75, the printed wiring board finally enters the outlet airlock gate 76, where it is cooled completely, for example also by a nitrogen supply, and the lock chamber is raised to normal pressure. This completes the soldering of the printed wiring board, but again the advantage for the whole soldering process is to use a solder that does not contain fluxing agents or that contains as little traces of the fluxing agent components as possible. It is. Furthermore, the soldering embodiment shown in FIG.
It is possible to simplify it somewhat without supplying plasma to it, and to configure it to exert a sufficient effect,
In this case, the preheating and pretreatment station 72 will receive its atmosphere from the brazing station 74.

In this way, by using essentially all the processing steps of brazing under low pressure and in a plasma gas atmosphere and in a process gas atmosphere, the use of fluxing agents is eliminated, and thus the release of FCKW A novel brazing process is provided which provides high quality brazed joints which are environmentally manufactured without the need for cleaning treatments, especially printed wiring boards which have been finish brazed.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05K 3/34 506 B23K 1/20 B23K 31/02 310

Claims (17)

(57) [Claims] 1. One or more of a supply step for supplying an electronic component to a printed wiring board for surface mounting, a preheating step preceding a soldering step, and a liquid phase solder generated from a solder bath. Carrying the printed wiring board along a flowing soldering surface of the soldering and performing a soldering operation by one or more soldering waves during the carrying, and after the soldering step to harden the solder. A soldering process for an electronic component with a printed wiring board according to a soldering process comprising a cooling step, wherein at least the soldering process itself is carried out under low pressure and under the plasma action of a process gas. Soldering a printed wiring board and an electronic component. 2. The brazing method according to claim 1, wherein the processing step preceding the brazing step or the processing step following the brazing step is performed under a low pressure equal to the brazing step itself. 3. The brazing method according to claim 1, which operates under a low pressure of 100 mbar or less. 4. The electronic component to be joined is pretreated by a plasma action generated in the preheating section during the preheating step or by a plasma action reaching into the preheating section.
Moreover, in order to form a plasma atmosphere in the preheating section,
4. The soldering method according to claim 1, wherein the same process gas is used for forming the soldering atmosphere. 5. The brazing method according to claim 4, wherein the atmosphere during the preheating stage is different from the gas atmosphere during the brazing process. 6. The brazing method according to claim 1, wherein a reducing and oxidizing process gas containing oxygen and hydrogen simultaneously is used as at least the plasma. 7. The process gas according to claim 6, wherein a mixture of 0.5 to 10% by volume of oxygen, 80 to 20% by volume of hydrogen and 20 to 80% by volume of CF ₄ , N ₂ or Ar is used as the process gas. Soldering method. 8. Glow discharge with microwave, high frequency and / or appropriate energy from the process gas
8. The brazing method according to claim 1, wherein a plasma action or plasma is generated. 9. The brazing method according to claim 1, wherein a plasma is generated directly around the brazing operation, that is, at the brazing site. 10. The brazing method according to claim 9, wherein the brazing bath is connected as a glow discharge cathode. 11. A plasma is generated outside the brazing equipment,
9. The brazing method according to claim 1, which is then fed to a brazing facility. 12. The brazing method according to claim 1, wherein the process gas is mixed before the treatment site. 13. The brazing method according to claim 1, wherein the process gas is provided as a finishing gas mixture. 14. The brazing method according to claim 1, wherein the preheating is performed via infrared light, microwaves or other suitable electromagnetic waves. 15. The soldering method according to claim 1, wherein the preheating is performed by inputting energy via a plasma. 16. A soldering station (4) and a plurality of other processing stations, ie a preheating station (28).
And a continuous soldering brazing facility with a cooling zone or advancing zone (5), surrounding the brazing station (4) and several other processing stations and hermetically sealed to the surroundings. Room (6) is provided,
And a means (18) for generating a low pressure in the equipment room and a brazing bath (4) at a site for generating a brazing wave (40, 42).
Either connect 8) as a cathode to an anode (49) located above the solder bath (48), or place a low pressure atmosphere in the region of the solder wave by placing a microwave transmitter or HF oscillator in the plasma. A continuous soldering type brazing facility, characterized in that a device for forming in a state is provided. 17. The brazing apparatus according to claim 16, wherein baffle members (78, 79) for blocking gas flow are provided between the individual stations.