JPH05259629A - Manufacture of printed circuit board coated with solder - Google Patents

Abstract

PURPOSE:To eliminate lead open failure to improve the reliability of part mounting by repeating a process for applying solder depositing composite and a process for heating it a plurality of times. CONSTITUTION:Paste solder depositing composite, composed of organic acid lead salt and tin power as principal components, is applied to a pad array on a printed circuit board, with the coat thickness 100mum. The composite is then heated at 215 deg.C for 2min to deposit solder. And these application and solder layer deposition processes, are repeated three times. This causes no lead open failure, improving the reliability of part mounting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solder-coated printed circuit board having a solder layer having a thickness necessary for soldering component leads on a pad.

[0002]

2. Description of the Related Art Conventionally, in order to mount surface mount components on a printed circuit board, cream solder is coated on a pad by a printing method, leads of the components are placed on the pad, and then the solder paste is heated to apply Soldering is performed by melting. However, recently, along with the miniaturization of the component lead arrangement pitch, the pad arrangement pitch has also become smaller,
When the pad arrangement pitch is 0.5 mm or less, it becomes difficult to print the cream solder, and soldering defects such as bridges frequently occur.

On the other hand, as a method for forming a solder layer on a pad of a printed circuit board, a metal powder having the largest ionization tendency (for example, tin powder) among the metals constituting the solder alloy.
And a method of utilizing a substitution reaction with an organic acid salt of another metal (for example, a lead salt of an organic acid) in the metal constituting the solder alloy (Japanese Patent Laid-Open No. 1-157796 etc.).

According to this method, for example, a paste solder deposition composition containing an organic acid lead salt and tin powder as main components is applied to a pad array portion of a printed circuit board in a solid coating form and heated to form an organic acid lead salt. This utilizes a phenomenon in which a solder alloy is selectively deposited on a pad due to a substitution reaction between tin powder and tin powder. According to this method, even if the pad arrangement pitch is 0.5 mm or less, the solder layer can be formed without causing a bridge.

[0005]

However, in this method, the paste-like solder deposition composition is solidly applied to the pad array portion to deposit the solder on each pad. Solder wraparound occurs on the pad from the solder deposition composition applied to the part of the above, and the amount of solder deposit due to this wraparound is not always uniform on each pad. It was found that the variation is likely to occur.

For example, conventionally, when the solder deposition composition is applied onto a pad to deposit a solder layer, the oxygen concentration is suppressed to 300 ppm or less in a nitrogen atmosphere reflow furnace, and the solder deposition temperature of the solder deposition composition ( (210 to 220 ° C) is heated for 40 to 50 seconds and then held at that temperature for a certain period of time.In this method, the solder layer thickness of each pad is the same as that of all pads. + 100% of the average thickness of
~ -50% variation occurs.

When the thickness of the solder layer deposited on the pad becomes non-uniform as described above, some leads cannot contact the solder layer when a component is mounted. Therefore, in a reflow furnace or a laser. Even if heated, some of the leads are not soldered, so-called lead open defects are likely to occur. It was also found that the variation in the thickness of the solder layer deposited on the pad is particularly likely to occur when the solder layer is formed thick on a pad having a small area, such as formation of solder bumps.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing a solder-coated printed circuit board which solves the above-mentioned problems. The first method is a pad for a printed circuit board. Above, a paste-like solder for precipitating solder by a substitution reaction of a powder of a metal having the largest ionization tendency among the metals forming the solder alloy and an organic acid salt of the other metal in the metal forming the solder alloy In a method for manufacturing a solder-coated printed circuit board, a solder composition having a thickness required for soldering of component leads is formed on a pad by applying a deposition composition and heating it at a solder deposition temperature, It is characterized in that the step of applying the composition and the step of heating the composition are repeated a plurality of times.

The amount of solder that wraps around the pad from the paste-like solder deposit composition applied to the portion other than the pad increases as the paste-like solder deposit composition is applied thicker.
Therefore, the thicker the paste-like solder deposition composition is applied, the greater the variation in the thickness of the deposited solder layer. Therefore, in order to reduce the amount of solder that wraps around on the pad and to reduce the variation in the thickness of the solder layer, the paste-like solder deposition composition is applied thinly to deposit the solder, and this is repeated multiple times. It is effective to secure the necessary thickness for attachment.

When the step of applying the solder depositing composition and the heating step are repeated a plurality of times, the thickness of one application of the solder depositing composition is preferably 200 μm or less, more preferably 100 μm or less.

A second method according to the present invention is to provide, on a pad of a printed circuit board, a powder of a metal having the highest ionization tendency among the metals constituting the solder alloy, and the other powders among the metals constituting the solder alloy. By applying a paste-like solder deposition composition that deposits solder by the substitution reaction of the metal with an organic acid salt and heating it at the solder deposition temperature, In the method of manufacturing a solder-coated printed circuit board for forming a solder layer, the heating time until the temperature rises to the solder deposition temperature is set to 20 seconds or less.

[0012] According to the results of various studies on the factors of variation in the thickness of the solder layer deposited on the pad, there is a relation with the heating rate when the paste-like solder deposition composition is applied and then heated. found. That is, the variation in the thickness of the solder layer tends to increase as the heating time to the solder deposition temperature increases, and if heating to the solder deposition temperature is performed for 20 seconds or less, the thickness of the solder layer of each pad It was clarified that can be suppressed within ± 20% of the average value of the solder layer thickness of all pads.

[0013]

EXAMPLES Examples of the present invention will be described in detail below.

Example 1 Pad size diameter 0.12 mm (circle), pad array pitch
200m with a bump forming pattern of 0.4mm and 120 pads
An m × 250 mm glass epoxy printed circuit board will be manufactured, and solder bumps with an average thickness of about 15 μm will be formed on the pads.

A paste-like solder deposition composition containing an organic acid lead salt and tin powder as main components was applied to the pad array portion of the printed circuit board and heated to deposit solder under the following two conditions. . After applying the solder deposition composition to a thickness of 100 μm,
The process of heating at 5 ° C. for 2 minutes to deposit the solder layer was repeated three times. After applying the solder deposition composition to a thickness of 300 μm,
The process of heating at 5 ° C. for 2 minutes to precipitate the solder layer was performed once.

The results of measuring the thickness of the solder bumps deposited on the pads by the above treatment with a surface roughness meter are as follows. Average thickness: 17 μm Minimum thickness: 11 μm Maximum thickness 26 μm Average thickness: 15 μm Minimum thickness: 5 μm Maximum thickness 75 μm

With the solder bumps, the component leads could be uniformly soldered, but with the solder bumps, the thickness of the solder bumps was not uniform, and some leads could not be soldered when the component leads were soldered. .

[0018]

[Example 2] A printed circuit board of 50 mm x 50 mm having a pad size of 0.20 mm x 1.0 mm and a pad array pitch of 0.3 mm for forming a 160-pin QFP type component mounting pad was manufactured, and an organic acid lead salt was formed in the pad array part. After applying a paste-like solder deposition composition consisting mainly of tin and tin powder to a thickness of 350 μm, place it on a hot plate in an atmosphere with an oxygen concentration of 300 ppm or less and heat it to deposit solder. It was performed under two conditions.

Printed circuit board temperature up to 215 ℃ 15
After raising the temperature in seconds, the temperature was maintained for 2 minutes. After raising the temperature of the printed circuit board to 215 ° C. in 45 seconds, the temperature was maintained for 2 minutes.

As a result of measuring the thickness of the solder layer deposited on the pad by the above treatment, the thickness of the solder layer of each pad is ± 20 with respect to the average value of the thickness of the solder layer of all pads.
The variation was within%, but then it was + 70%-
The variation was in the range of 40%. Also, according to the result of mounting components and checking the occurrence rate of lead open defects, in n = 3200 pins, the occurrence of lead open defects was not recognized, but in n = 3200 pins, the occurrence rate of lead open defects was found. Was 0.5%.

[0021]

As described above, according to the present invention, on the pad of the printed circuit board, the powder of the metal having the largest ionization tendency among the metals forming the solder alloy and the metal forming the solder alloy When the solder layer is formed by the substitution reaction of other metal with organic acid salt, it is possible to reduce the variation in the thickness of the solder layer, and as a result, there is no lead-open defect when mounting components. There is an advantage that components can be mounted with high reliability.

Front page continuation (72) Izumi Kosuge 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Yuichi Obara 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Industrial Co., Ltd. (72) Inventor Kenichi Fuse 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Hisao Irie 4 Harima Kasei, 671 Mizuzushi, Noguchi Town, Kakogawa City, Hyogo Prefecture Central Research Institute Co., Ltd. (72) Inventor Satoshi Kumamoto 4 671 Mizusui, Noguchi-cho, Kakogawa-shi, Hyogo 4 at Harima Kasei Co., Ltd. (72) Inventor Takahiro Fujiwara 4-671 Mizusui, Noguchi-cho, Kakogawa-shi, Hyogo Harima Kasei Co., Ltd. Central Research Institute (72) Inventor Masanao Kono 4 671 Mizusui, Noguchi-cho, Kakogawa City, Hyogo Prefecture

Claims (4)

[Claims] 1. On a pad of a printed circuit board, a powder of a metal having the largest ionization tendency among the metals forming the solder alloy and an organic acid salt of the other metal in the metal forming the solder alloy. Solder coat print that forms a solder layer with a thickness necessary for soldering component leads on a pad by applying a paste-like solder deposition composition that deposits solder by a substitution reaction and heating it at the solder deposition temperature. A method for producing a solder-coated printed circuit board, characterized in that the step of applying the solder deposition composition and the step of heating are repeated a plurality of times in the method for producing a circuit board. 2. The thickness of one application of the solder deposition composition is 200 μm.
The method for manufacturing a solder-coated printed circuit board according to claim 1, wherein the method is not more than m. 3. The thickness of one application of the solder deposition composition is 100 μm.
The method for manufacturing a solder-coated printed circuit board according to claim 1, wherein the method is not more than m. 4. A powder of a metal having the highest ionization tendency among the metals forming the solder alloy and an organic acid salt of the other metal in the metal forming the solder alloy on the pad of the printed circuit board. Solder coat print that forms a solder layer with a thickness necessary for soldering component leads on a pad by applying a paste-like solder deposition composition that deposits solder by a substitution reaction and heating it at the solder deposition temperature. In the method for manufacturing a circuit board, the method for manufacturing a solder-coated printed circuit board is characterized in that the heating time until the temperature is raised to the solder deposition temperature is 20 seconds or less.