JPH01231396A - Soldering method for printed wiring board - Google Patents

Abstract

PURPOSE:To eliminate un-soldered sections and to improve reliability of soldering, by a method wherein after a primary soldering treatment is performed, a printed wiring board is changed in its direction, and subsequently the soldering surface of the printed wiring board is again treated with a secondary soldering treatment. CONSTITUTION:After a primary soldering treatment is performed, change of direction is performed in a printed wiring board so that chip components are directed in the direction different from that during the primary soldering treatment. At this time, in the case where the front and the back of the chip components are reversed, the direction of the printed wiring board is changed by 180 degrees. On the other hand, in the case where the chip components disposed perpendicular to the advance direction of the printed wiring board is only directed in the parallel direction therewith, the direction of the printed wiring board is changed by 90 degrees. After change of the direction is performed in such way, the printed wiring board is fed to a secondary soldering apparatus, and flux coating and preheating are performed in fluxers 2, 7 and preheaters 3, 8, respectively. In a high wave soldering vessel 11, the positions in the printed wiring board difficult for solder to deposite thereto are directed in the direction in which it is easy for solder to deposite thereto. Therefore, solder perfectly penetrates the un-soldered positions provided during the primary soldering treatment, so that there are no un-soldered positions in the printed wiring board.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to soldering of printed circuit boards, and particularly to a method of soldering a printed circuit board on which chip components are mounted by bringing it into contact with molten solder.

[Conventional technology]

A common method for soldering printed circuit boards with leaded electronic components is flux application, preheating, and molten solder contact in a static solder bath or a gentle wave jet of solder pot. However, this soldering method cannot be used for a printed circuit board on which chip components are mounted because it generates a large amount of unsolder to which no solder adheres. This is because the soldering part of the chip component and the printed circuit board form a corner at a right angle, and therefore, in a solder bath used for soldering electronic components with leads, molten solder cannot penetrate into the corner.

Therefore, in recent years, as a method for soldering printed circuit boards on which chip components are mounted (hereinafter referred to as "chip component soldering"), a double wave solder bath has been used for contact with molten solder.

A double wave solder bath is equipped with a rough wave solder bath that jets rough molten solder and a finishing solder bath that jets calm molten solder.

The method for soldering chip components using a double wave soldering bath is as shown in FIG. This is carried out by sequentially contacting the molten solder flowing from the finishing solder tank 12. At this time, in a rough wave soldering bath, molten solder can penetrate into right-angled soldering parts, but because the jet waves are rough, many soldering defects such as icicles and bridges occur. Therefore, the icicles and bridges that occur in the rough wave solder bath are removed using a finishing solder bath with calm jet waves.

[Problem to be solved by the invention]

The conventional soldering method for chip components is revolutionary in that it allows molten solder to penetrate into the soldered parts of chip components in a rough wave soldering bath, but even this method cannot completely eliminate unsolder. - An object of the present invention is to provide a soldering method that can eliminate unsoldered parts when soldering chip components.

[Means to solve the problem]

When soldering chip components, unsoldered parts often occur behind the chip components mounted generally parallel to the direction in which the printed circuit board travels. The reason for this is that the soldering area at the front of the chip component is open to the jet stream of the rough wave soldering bath, so molten solder easily enters the soldering area at the front, but the soldering area at the back Since the opening of the attachment portion faces backward with respect to the jet flow, it becomes difficult for molten solder to penetrate, and unsolder often occurs.

However, unsoldered parts during soldering of chip parts are not limited to the rear part of the printed circuit board in the direction of movement, but can occur at various locations depending on the mounting state of the chip parts and the type of the chip parts. In other words, if chip components are mounted at a high density or if there are large chip components, the path through which molten solder flows will be blocked or shaded, making it impossible for molten solder to penetrate into the soldering area. .

The inventor of the present invention discovered that the directionality of a printed circuit board is the cause of unsolder, and completed the present invention by noting that if the problem of directionality is solved, unsolder will disappear.

The present invention performs a primary soldering process such as flux application, preheating, and contact with a jet of molten solder on the soldering surface of a printed circuit board, then changes the direction of the printed circuit board, and performs the soldering process on the printed circuit board. This method of soldering a printed circuit board is characterized by performing a secondary soldering process such as re-applying flux to the surface, preheating, contact with molten solder of a rough wave jet, and contact with molten solder of a radio wave jet.

〔Example〕

The primary soldering device 1 that performs the primary soldering process consists of a fluxer 2, a pre-heater 3, a rough wave soldering bath 4 that jets molten solder in rough waves, and a cooling device 815, and a secondary soldering device that performs the secondary soldering process. 6 consists of a fluxer 7, a pre-heater 8, a double wave soldering bath 9 and a cooler 10. Double wave solder bath 9
There is a rough wave solder tank 11 where molten solder from rough waves is jetted.
Finishing solder bath 12 that jets molten solder in quiet waves
is installed. The rough wave solder bath used in the present invention is one in which the jet of molten solder is rough or vibrates.
Means for roughening the molten solder include mechanical roughening from the outside, roughening with the force of a jet, or vibration with ultrasonic waves. - A direction changing device 13 is installed between the secondary soldering device rIiI and the secondary soldering device 6.

In the soldering method of the present invention using the above device, a printed circuit board (not shown) on which chip components are mounted enters the primary soldering device 1 as shown by the arrow, is coated with flux by a fluxer 2, is preheated by a pre-heater 3, The rough wave solder bath 4 contacts the molten solder flowing in the rough wave jet. The direction of the printed circuit board that has been subjected to the primary soldering process in this manner is changed by the direction changing device 13. The printed circuit board whose direction has been changed enters a secondary soldering device 6, and is subjected to secondary soldering processing in a fluxer 7, a preheater 8, a rough wave solder pot 11 of a double wave solder bath 9, and a finishing solder bath 12.

Next, the soldering processing state in the above soldering method will be explained.

In the rough wave soldering bath during the primary soldering process, molten solder adheres to the soldered parts of the chip components at the front in the direction of travel of the printed circuit board, where solder tends to adhere, and to locations that are not affected by other chip components. A large amount of unsolder occurs in the soldered parts of chip components that are at the rear in the direction of movement of the chip, and in locations that are affected by other chip components. Therefore, the direction of the printed circuit board after the second soldering process is changed so that the direction of the chip components is different from that during the first soldering process. At this time, if you want to change the front and back of the chip components, turn the printed circuit board 180 degrees, and if you simply want to turn the chip components that were oriented vertically to the direction of travel of the printed circuit board horizontally, turn the printed circuit board 90 degrees. After the direction has been changed, the printed circuit board is entered into a secondary soldering device, where it is coated with flux using a fluxer and preheated using a preheater. This flux application is to supplement the flux that was washed away by the molten solder in the rough wave solder bath during the primary soldering process, and the preheating is to reheat the printed circuit board that has been cooled by flux application with a fluxer and to heat it again for the next melting process. Preparing for solder contact 4. Rough waves during secondary soldering process In the soldering bath, the parts of the printed circuit board where it is difficult for solder to adhere are in a direction where it is easy for solder to adhere. The solder has completely penetrated into the previously soldered areas, and there is no unsoldered area on the printed circuit board. However, even in the rough wave soldering bath, defects such as icicles and bridges occur in the soldered portion, so these defects are removed in the next finishing solder bath.

〔Effect of the invention〕

According to the present invention, since it is possible to completely eliminate unsolder on a printed circuit board on which chip components are mounted, where it has conventionally been considered impossible to eliminate unsoldered parts, reliable soldered parts can be obtained.

[Brief explanation of the drawing]

Claims (1)

[Claims] Flux is applied to the soldering surface of a printed circuit board. After performing the primary soldering process such as preheating and contact with the molten solder of the rough wave jet, the direction of the printed circuit board is changed, flux is applied again to the soldering surface of the printed circuit board, preheating, and the molten solder of the rough wave jet is performed. A method for soldering a printed circuit board, characterized by performing a secondary soldering process such as contact with a static wave jet and contact with molten solder of a static wave jet.