WO2008006700A1

WO2008006700A1 - Wave soldering system for soldering electronic components on a printed circuit board

Info

Publication number: WO2008006700A1
Application number: PCT/EP2007/056440
Authority: WO
Inventors: Dietmar Birgel; Franz Glatz
Original assignee: Endress+Hauser Gmbh+Co.Kg
Priority date: 2006-07-10
Filing date: 2007-06-27
Publication date: 2008-01-17
Also published as: DE102006032051A1; DE102006032051B4

Abstract

In known wave soldering systems, the liquid solder is usually covered, in order to avoid or at least reduce the drawbacks associated with the oxidation of the solder. For typical tin-lead solder, a simple oil is used as the covering, or alternatively a nitrogen covering is used (particularly for higher melting points). However, oil coverings for lead-free solder fail as a result of the higher melting points and nitrogen coverings are problematical at temperatures over 260°C as they require a high nitrogen throughput and a particular degree of purity. The invention discloses a perfluorinated polyether with a boiling point of over 260°C at atmospheric pressure as an effective covering medium (62) for the solder (56) in the crucible (52), said polyether being easy to produce and cost-effective. A covering (62) of this type can also be used in conjunction with a nitrogen covering (64). A condensate trap can also be employed (68) to collect any evaporated covering medium.

Description

description

Wave soldering machine for soldering electronic components on one

circuit board

The invention relates to a wave soldering for soldering electronic components on a printed circuit board.

It is known to solder electronic assemblies or printed circuit boards with wave soldering, semi or fully automatic. After the desired components have been mounted on such a circuit board, a solder side of the circuit board is first wetted with a flux. Thereafter, the circuit board and the components are preheated to evaporate a proportion of solvent in the flux and to avoid a temperature delay of the assembly by a too steep temperature rise during subsequent soldering. The actual soldering is achieved in such Wellenlötanlagen by a solder wave, over which the circuit board is driven. The solder wave is generated by pumping liquid solder, which is in a heatable crucible, through a gap.

The soldering temperature is for lead-containing solders to about 240 - 250 ⁰ C, for lead-free solders usually more than 260 ⁰ C.

The shape of the solder wave is application-dependent and determines the quality of the desired solder joint. In many cases, two waves are used directly behind one another to cope with even more complex soldering situations. So surface-mounted electronic components (so-called SMD components) on a solder side of the circuit board together with connection pins of wired components (so-called THT components) located on the other side of the circuit board, in the same work step can be securely soldered to the circuit board.

Another variant of the wave soldering is the so-called selective wave soldering. Here, not the whole circuit board or assembly, but only a small part thereof is soldered by means of only a few millimeters wide solder wave.

Typically, a cover of the solder is provided today during wave soldering in order to avoid the disadvantages associated with oxidation of the solder, or at least to significantly reduce. As cover of the solder, a simple oil has hitherto been used in typical tin-lead solders with melting points up to 180 ^° C. Alternatively, and especially at higher melting points, a nitrogen blanket is also provided today.

A disadvantage of the oil covers described above is that they are lead-free Solders with melting points above 260 ⁰ C fail. Nitrogen covers are problematic at the temperatures considered above 260 ⁰ C, as they have a special

Require purity and high nitrogen throughput. Because of the required high throughput is only an on-site nitrogen production from the

Ambient air economically, which in turn often does not offer the required purity of

Can provide nitrogen coverage. The invention is therefore based on the object for wave soldering with lead-free

Solve a cover to create that is easy to implement and economical to operate. This object is achieved by a Wellenlötanlage according to the invention for

Solder electronic components on a circuit board, which wave soldering a

Includes crucible for receiving a solder, wherein a surface of the solder is covered in the crucible during the soldering process of a perfluorinated polyether as a covering medium and thus minimized oxidation of the solder, wherein the covering medium at ambient pressure has a boiling point above 260 ⁰ C. In another embodiment of the wave soldering according to the invention a further cover with nitrogen is provided on the covering. In yet another embodiment of the wave soldering system according to the invention, the covering medium is stored in a tank. Yet another embodiment of the wave soldering system according to the invention comprises a condensate trap for vaporized covering medium. In a further embodiment of the wave soldering invention, the

Condensate of the vaporized Abdeckmediums collected and is traceable to the crucible. In yet another embodiment of the wave soldering system according to the invention, the collected condensate of the vaporized Abdeckmediums is cleaned before being returned to the crucible. Yet another embodiment of the wave soldering system according to the invention comprises a sensor for controlling a layer thickness of the covering medium on the

Lot in the crucible. The advantage of the invention is the fact that it is easy to implement and that they have at least the same advantages as the conventional covers of the

Lotes offers: improved solder joints due to higher wetting speeds, significantly reduced solder consumption by reducing the oxides (scabies), reduced flux consumption, mild activated flux. Cleanliness of printed circuit boards, reduced maintenance; and environmentally friendly soldering with lead-free solders.

The invention will be described and explained in more detail below, reference being made to the accompanying drawings. Showing:

Fig. 1 is a schematic sectional view of a conventional wave soldering machine; and

Fig. 2 is a schematic sectional view of a particular embodiment of the invention.

In Fig. 1, a wave soldering system 10 is shown schematically, as used heretofore. In a lower region of a crucible 12, a heater 14 is provided, which holds for soldering a Lot 16 located in the crucible 12, today usually a tin-lead solder, at a temperature just above the melting point of the solder 16. For the soldering process, the molten solder is pressed through a slot nozzle 18 shown schematically here in the crucible 12 and directed upwards, mostly pumped. Upon exit of the solder 16 from the slot 18, a solder wave 20 is generated, as shown in FIG. 1 illustrates.

About a running on rollers 22 transport device 24, which is shown here only indicated, populated printed circuit boards 26 are brought to the wave soldering machine 10. For simplicity, only two printed circuit boards 26 are shown schematically in Fig. 1. SMD components 30 have usually already been soldered to the respective upper sides 28 of the printed circuit boards 26. For the soldering process considered here in the Wellenlötanlage 10 are on the upper sides 28 of the printed circuit boards 26 optionally also wired components, THT components 32, equipped, as illustrated in Fig. 1, the connecting pins 34 have been inserted in corresponding connection holes through the circuit boards 26 therethrough ,

On the respective Lötseiten 36 of the circuit boards 26 SMD components 38 are also equipped for the wave soldering process considered here, which are soldered to the solder wave 20 as well as from the respective tops 28 of the printed circuit boards 26 pushed through and on the Lötseiten 36 of the printed circuit boards 26 projecting terminal pins 34 of the THT components 32. The transport device 24 is set so that they can be run over by the circuit boards 26 so that the soldering sides 36 of the circuit boards 26 are wetted by the solder wave 20 in the desired manner, but the solder wave 20 passes on the tops 28 of the printed circuit boards 26.

As already mentioned, provide oxidation products of the solder 16 a problem The simplest cover used to date in the crucible 12 molten solder 16 is an oil cover 40, as illustrated in Fig. 1. Such an oil cover can be realized in the simplest way with a relatively simple oil, such as peanut oil, which can be used with a boiling point of about 210 ⁰ C for leaded solders. With increasing melting temperatures of the solder, unlike lead-free solders, higher-grade oils with a higher boiling point are required, which then also rise above average in price.

As an alternative to an oil cover of the solder has been and is a nitrogen blanket is used, which is not shown in Fig. 1.

2 is a schematic representation of an embodiment of a wave soldering system 50 according to the invention. As in the case of the wave soldering system shown in FIG. 1, a heater 54 is also provided here in a lower region of a crucible 52, the solder for brazing a solder located in the crucible 52 56, preferably a lead-free solder, at a temperature just above the melting point of the solder 56 holds. For the soldering process, the molten solder 56 is pressed by a schematically shown here and obliquely upward slot nozzle 58 in the crucible 52, mostly pumped. Upon exit of the solder 56 from the slot 58, a solder wave 60 is generated as illustrated in FIG.

A, as shown in Fig. 1, on rollers running transport device, are brought with the assembled printed circuit boards to the solder wave 60, can be used in the embodiment of the wave soldering machine 50 of FIG. 2. It is not shown for clarity in Fig. 2. In order to avoid oxidation, a special covering medium 62 is provided here to cover the solder 56. In this covering medium 62 according to the invention is a perfluorinated polyether having a boiling point above 260 ⁰ C at ambient pressure. Perfluorinated polyethers which are suitable for the invention are used, for example, in so-called vapor-phase soldering as a heat transfer medium.

In experiments with the invention with various lead-free solders 56 have perfluorinated polyether, which are manufactured by the company Solvay Solexis and are available under the name "GALDEN" proved to be suitable. The perfluorinated polyether type GALDEN® are currently available with different boiling points up to 270 ⁰ C. Ideally, however, with the invention, a perfluorinated polyether having a boiling point of about 300 ⁰ C is used to keep evaporation of the covering medium in a three-layer industrial soldering operation with lead-free solder below 5% per day. In addition to the masking medium 62 made of perfluorinated polyether in the embodiment of the wave soldering system 50 according to the invention shown in Fig. 2 nor a nitrogen cover 64 is provided, which is located between the covering medium 62 of polyether and a lid 52 disposed above the crucible 52. This nitrogen blanket 64 is not essential to the invention because the polyether capping medium 62 is already very efficient. However, it is advisable, especially when upgrading existing wave soldering with nitrogen cover on lead-free solder to maintain the nitrogen blanket and to use together with the inventive cover medium 62 made of polyether.

Although the previously tested Abdeckmedien 62 have proven to be productive from perfluorinated polyethers and evaporate very low at appropriately selected boiling point in the soldering process with lead-free solder, a condensate trap 68 is provided in the embodiment shown in Fig. 2, the Wellenlötanlage 50 of the invention the crucible 52 as completely as possible covered, as illustrated in Fig. 2. Evaporated cover medium 62 of perfluorinated polyether condenses on the condensate trap 68 and drains off to the sides of the condensate trap 68 because of a roof-like construction. If backflow of the condensed polyether cover medium 62 from the condensate trap 68 into the crucible 52 does not function as desired because of the cover 66 over the nitrogen cover 64, a catcher 70 is recommended in the lower portion of the condensate trap 68 surrounding the condensed cover medium 62 of polyether to collect and return by means of a suction device 72 in the crucible 52.

The covering medium 62 made of perfluorinated polyether is usefully stored outside the crucible in a storage container 74. For semi-or fully automatic refilling of the reservoir 74 is connected via a line 76 to a pump 78, with which the covering medium 62 is pumped from polyether from the reservoir 74 via a further line 80 into an inlet 82 and then into the crucible 52. The suction device 72 for the collected in the collecting device 70 condensed covering medium 62 made of polyether is connected to a line 84 to the conduit 80 just before it opens into the inlet 82. It is of course also possible to connect the suction device 72 directly to the reservoir 74 in order to bring the condensed polyether back into it.

If there is a risk of contamination of the covering medium 62, it makes sense condensed Abdeckmediums 62 before returning to the crucible 52nd to clean.

A great advantage of the perfluorinated polyether used in the invention as covering medium 62 in the Wellenlötanlage 50 shown in Fig. 2 is that the covering 62 also gets there and covers the solder 56, where the nitrogen cover is not sufficient: ie in a neck of Slot nozzle 58. Especially with a very narrow slot of the slot 58 may come through oxidation products for partial clogging and thus to an uneven solder wave 60. Should it unexpectedly come to fine oxidation products on the solder 56 in the crucible 52, it has been found in that the perfluorinated polyether as covering medium 62 can bind these fine oxidation products. This also achieves a more even solder wave.

[0033] List of Reference Numerals:

[0034]

Table 1

Claims

claims

1. Wave soldering for soldering electronic components on a circuit board, which wave soldering (50) comprises a crucible (52) for receiving a solder (56), characterized in that a surface of the solder (56) in the crucible (52) during covered by a perfluorinated polyether as covering medium (62) and thus minimizing oxidation of the solder (56), wherein the covering medium (62) at ambient pressure has a boiling point above 260 ⁰ C.

2. wave soldering machine according to claim 1, characterized in that above the

Covering medium (62) is provided a further cover (64) with nitrogen.

3. wave soldering machine according to one of claims 1 or 2, characterized in that the covering medium (62) in a tank (74) is stored.

4. Wave soldering machine according to one of claims 1 to 3, characterized in that it comprises a condensate trap (68) for evaporated covering medium (62).

5. wave soldering machine according to claim 4, characterized in that the

Condensate of the vaporized covering medium (62) is collected and in the crucible (52) is traceable.

6. Wellenlötanlage according to claim 5, characterized in that the collected condensate of the evaporated Abdeckmediums (62) before being returned to the crucible (52) is cleaned.

7. wave soldering machine according to one of claims 1 to 6, characterized in that the covering medium (62) is a perfluorinated polyether.