JPH0582955A - Ink-form solder for printing and fine soldering method - Google Patents

Abstract

PURPOSE:To enable printing to a pattern section having fine dimensions by using ink-form solder for printing, in which fine solder is dispersed into a dispersion medium. CONSTITUTION:Ink-form solder for printing, in which fine solder having the low degree of oxidation is dispersed into a dispersion medium adjusted so that the whole dispersion medium is evaporated at a soldering temperature in a vacuum, is used. Printing is conducted to a fine pattern section on a substrate by the ink-form solder for printing, and a holding substrate 2, to which an electronic part is set up, is placed on a chain conveyor 7 in a vacuum tank 1. The holding substrate 2 is transferred to a vacuum reflow soldering heating section in the vacuum tank 1. Exhaust is performed by a rotary vacuum pump 6 in the heating section, heating is started by an infrared heater 3, and a solder pattern is thermally fused. The holding substrate 2, to which vacuum reflow soldering is completed, is passed through a parting plate 15 and conveyed to a cooling chamber with a water-cooling unit 9 and a cooling fan 8, and cooled by a gas fan in a nitrogen atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing ink-like solder and a vacuum reflow fine soldering method used for soldering a joint having a fine dimension such as a printed wiring board or a hybrid integrated circuit board. is there.

[0002]

2. Description of the Related Art When surface-mounting electronic parts on a holding substrate, the conventional method is a batch reflow soldering method, which uses a hot air reflow furnace with far infrared rays, a nitrogen atmosphere reflow furnace, a vapor face reflow device, etc. Has been. As a batch reflow soldering method for surface mounting in vacuum, there are methods disclosed in Japanese Patent Laid-Open Nos. 63-250898 and 2-137393.

In the above-mentioned batch reflow soldering method for surface mounting in vacuum, cream solder, which has been conventionally used, is applied to the substrate pattern surface by the screen printing method. This cream solder is
Originally intended for reflow soldering under atmospheric pressure,
No special soldering method for reflow soldering in vacuum has been proposed yet.

[0004]

Conventionally used cream solders include solder powder having a particle size of 250 to 350 mesh and an average particle size of 40 to 50 μm, rosin as a base, amine hydrochloride as an activator, and the like. In addition to the flux component to which an organic halogen compound is added, it is composed of an organic solvent, a wax-like compound as a printing property (thixotropic property) adjuster, etc., and is molded into a cream.

When this conventional cream solder is heated in a vacuum, components other than the solder powder partially evaporate or thermally decompose, so that corrosive halides are generated around the soldered portion or printed. Scatter on circuits. Therefore, the corrosive residue is attached to the substrate surface or the inner wall of the vacuum chamber. Therefore, the substrate contaminated with the corrosive substance must be cleaned without fail, and the inside of the vacuum chamber must be cleaned frequently.

As the conventional cream solder, powder solder having a large particle size is used as described above, and 50,000 to 100,000 is used.
Since it is a cream-like substance having a viscosity as high as CPS, it cannot be printed on a pattern portion having a fine dimension. That is, in the conventional product, the pitch of the pattern to which the solder can be applied is about 500 μm and the width is about 200 μm. Therefore, there is a limit to increase the packaging density.

The present invention has been made in view of the above problems, and the purpose thereof is (1) cleaning is required because a corrosive residue does not adhere to a substrate surface or an inner wall of a vacuum chamber. (2) To provide a printing ink-like solder and a vacuum reflow fine soldering method capable of printing on a finely sized pattern portion and increasing the packaging density.

[0008]

Means for Solving the Problem and Its Action As a result of various studies aimed at achieving the above object, the present inventor has found that fine solder powder having a low degree of oxidation is dispersed in a dispersion medium which can be easily evaporated. The above-mentioned object could be achieved by paying attention to the ink-like solder for use.

That is, the gist of the present invention is a dispersion medium containing an organic solvent as a main component, which is adjusted so that all of it is evaporated at a soldering temperature in vacuum. Ink-like solder for printing, which is characterized in that it is dispersed, further in the method of soldering electronic components in a fine dimension on the holding substrate, a dispersion medium containing an organic solvent as a main component, in a vacuum In a dispersion medium adjusted so that all of it evaporates at the soldering temperature, using a printing ink-like solder in which fine powdered solder having a low degree of oxidation is dispersed, a step of printing a solder pattern on the holding substrate, and A step of mounting an electronic component on the solder pattern, a step of heating and melting the solder pattern at a solder reflow temperature in a vacuum, and a step of cooling the solder pattern. A fine soldering method characterized by comprising a step of fixing the pattern and the electronic component.

The ink-like solder for printing in the present invention is
A fine powder solder having a low degree of oxidation is dispersed in a dispersion medium, and the dispersion medium contains an organic solvent as a main component, and the main organic solvent used in the present invention is glycerin, 1 -Alcohols such as octanol, glycols such as diethylene glycol and methylpropylene glycol, organic acid esters such as dioctyl phthalate, cellosolve solvents such as butyl cellosolve and methyl cellosolve, and distilled tall oil which is a vegetable oil.

The above-mentioned dispersion medium is prepared by adding steam-distilled resinous substances such as tall rosin and alkyd resin, or higher alcohols such as pentaerythritol and cetyl alcohol, into one or more of the above organic solvents, if necessary. Any of the following second components is added. And as the activator component, amines such as diethanolamine,
A volatile halogen compound such as dimethylamine hydrochloride or hydrazine hydrochloride is added as necessary.

Further, in the present invention, the above dispersion medium is added in an amount of 50 to 25 in a vacuum at a pressure of 1 mmHg or less.
It is adjusted to consist of components that evaporate at a temperature of 0 ° C. As a result, all the components of the dispersion medium evaporate at the soldering temperature in vacuum, so that even a halogen compound does not leave a residue and cleaning is unnecessary. Then, the evaporated dispersion medium can be recovered and reused as described later. Further, it is necessary to adjust the component composition of this dispersion medium so that, when fine powder solder is dispersed, it becomes a low-viscosity printing ink-like solder as described later. The activator component is used to enhance the reflow property, that is, the meltability of the solder during soldering.

Next, in the above dispersion medium, the average particle size is 10 μm.
m or less and the amount of oxygen adsorbed is 300 ppm per 1 g
An ink-like solder for printing is obtained by dispersing the following fine powder solder having a tin-lead eutectic composition. This fine-powder solder is obtained by subjecting a tin-lead alloy having a eutectic composition to a high-purity inert gas atmosphere by high-pressure gas atomization to obtain an average particle size of
It is obtained by molding into a fine powder having a size of not more than μm. The reason why the oxygen adsorption amount is 300 ppm or less per 1 g is
This is to improve the meltability of the solder. Next, regarding the mixing ratio of the fine powder solder to the dispersion medium, this is mixed and dispersed in the dispersion medium at a ratio of 50 to 90% by weight. Then, as described above, the viscosity is adjusted to 500 cps or less in combination with the component composition of the dispersion medium.

As described above, the ink-like solder for printing according to the present invention uses fine powdery solder and has a low viscosity and is oily, so that the printing characteristics are good, and high precision and high resolution screen printing is possible. Becomes That is, if a squeegee is performed with this ink-like solder using a metal screen, 10
It is possible to print with a width of 50 μm at a pitch of 0 μm, and about half of the ink printing thickness of 20 to 40 μm is the thickness of fine powder. Therefore, after the ink-like solder is printed on the printed wiring board having the pattern portion for fine bonding, a small electronic component or a multi-pin narrow-pitch four-direction flat package L
By mounting SI or the like, heating in a vacuum for reflow soldering, and evaporating and extinguishing the dispersion medium, the drawbacks of the prior art can be solved. The ink-like solder for printing in the present invention can be printed by gravure printing or intaglio printing as well as the above metal screen printing.

Further, if reflow soldering is performed in a vacuum using ink solder or cream solder dedicated to heating in a vacuum, the storage gas in the solder particles is also released into the vacuum at the time of reflow as the dispersion medium evaporates. Defects such as voids and pinholes are prevented, and the reliability of the joint is improved.

[0016]

EXAMPLES The ink-like solder for printing and the vacuum reflow fine soldering method according to the present invention will be described based on the following examples. Example 1. Glycerin was used as the organic solvent and
6% by weight, pentaerythritol 18.5% by weight,
A dispersion medium was prepared by mixing diethanolamine as an activator component at a ratio of 5.5% by weight. This dispersion medium completely evaporates and disappears at 200 ° C. or lower in a vacuum with a pressure of 1 mmHg or lower. Next, in this dispersion medium, an average particle size of 5μ
A fine powder solder composed of a tin-lead alloy having a eutectic composition and having an oxygen adsorption amount of 250 ppm per 1 g of m was added and mixed at a proportion of 85% by weight and dispersed to prepare a printing ink-like solder. And the viscosity of this ink-like solder is 150 cp
It was s.

Embodiment 2. Next, a vacuum reflow fine soldering method according to the present invention will be described with reference to FIG. A holding substrate on which electronic components are mounted after printing (printing with a pitch of 100 μm and a width of 50 μm) on a fine pattern portion on the substrate using the ink-like solder for printing adjusted in the above Example 1 (printing with a pitch of 100 μm) 2 is placed on the chain conveyor 7 in the vacuum chamber 1. In the figure, 11 is a drive motor for the conveyor. Next, this holding substrate 2
Is transferred by the chain conveyor 7 to the vacuum reflow solder addition heat section in the vacuum tank 1.

In the heating section in the vacuum chamber 1, the rotary vacuum pump 6 starts exhausting. Here, the degree of vacuum, the atmosphere, and the heating temperature are controlled in conjunction with each other. First, the pressure is sufficiently reduced to the level of 10 ⁻³ mmHg, and then high-purity nitrogen gas is blown from the nitrogen gas introduction valve 14 to raise the pressure to atmospheric pressure. After that, when the gas is exhausted again and the pressure is reduced to about 500 mmHg, the infrared heater 3 is input and heating is started.

When heated, the evaporation of the dispersion medium becomes active 1
Since the pressure in the heating part increases from around 50 ° C, exhaust is performed and the pressure is reduced to about 10 to 100 mmHg. In the range of the reflow temperature of 190 to 230 ° C, complete evaporation of the dispersion medium and good melt flow of the solder are performed. In order to generate it, vacuum evacuation is further performed up to 10 ⁻³ mmHg level.

When an electronic component such as an electrolytic capacitor or a flat package LSI, which is vulnerable to heat and vacuum pressure and may be destroyed, is mounted on the holding substrate, a vacuum of about 1 mmHg at 100 to 150 ° C. It is preferable that the dispersion medium is evaporated and extinguished by heating and holding it therein, and then high-purity nitrogen gas is introduced into the heating portion up to near atmospheric pressure, and reflow soldering is performed under that pressure.

After holding the vacuum reflow soldering, the holding substrate 2 is left to stand until it reaches a temperature of 180 ° C. or lower, and then passed through the sluice valve 15 by the chain conveyor 7 and provided with a water cooling unit 9 and a cooling fan 8. Transfer to a cooling chamber and cool with a gas fan in a nitrogen atmosphere at atmospheric pressure. The components of the dispersion medium that evaporate during heating are introduced from the dispersion medium collector 4 adjusted to have a vacuum pressure gradient to the water cooling trap 5 for recovery, and are liquefied and recovered. 1 in FIG.
Reference numeral 0 is a reflector, 12 is a Pirani compound gauge, and 13 is a cooling fan drive motor.

As described above, in the vacuum reflow fine soldering method using the ink-like solder for printing according to the present invention, the evaporated dispersion medium of the ink-like solder is recovered, so that it can be reused. it can. Therefore, the treatment process can be a closed system and leads to effective use of resources. Moreover, since the method according to the present invention is soldering in a vacuum, oxidation during heating is prevented.

Next, the printing ink-like solder according to the present invention can be used to perform solder coating treatment on the fine pattern portion by the same method and apparatus as those described in this embodiment. That is, it is possible to process at a lower cost and with higher productivity than the plating method or the vacuum deposition method.
For example, a bare chip IC can be applied as a micro bump forming method. Also, depending on the particle size of the solder powder,
It is also possible to make cream solder for vacuum reflow soldering, and to perform vacuum reflow soldering of surface mount boards on which ultra-small chip parts and ordinary electronic parts are mixed, without the need for cleaning operations. Becomes

[0024]

According to the ink-like solder for printing and the vacuum reflow fine soldering method according to the present invention, it is possible to use a 5 μm pitch with a pitch of 100 μm, which is considered impossible by the conventional technique.
Since it is possible to print on a pattern portion having a fine dimension of 0 μm width and fine soldering is possible, the packaging density can be dramatically improved. Then, since all the components of the dispersion medium of the ink-like solder are evaporated and collected, corrosive residues do not adhere to the substrate surface or the inner wall of the vacuum chamber, and cleaning is not necessary. Furthermore, the recovered dispersion medium can be reused, which leads to effective use of resources. In addition, since the treatment process can be a closed system, no pollution occurs and the technique is extremely practical.

Next, according to the present invention, it can be applied as a method for coating a pre-solder on a fine pattern portion, and the bare chip I can be applied without using a plating method or a vacuum deposition method.
It is also possible to perform micro bump formation of C and micro joining of TAB lead portions.

[Brief description of drawings]

FIG. 1 is a front view of an apparatus for carrying out a vacuum reflow fine soldering method according to the present invention.

[Explanation of symbols]

 1 vacuum tank 2 holding substrate on which electronic parts are mounted 3 infrared heater 4 dispersion medium collector 5 water cooling trap for dispersion medium recovery 6 rotary vacuum pump 7 chain conveyor 8 cooling fan 9 water cooling unit 10 reflector 11 chain drive motor 12 Pirani coupling Total 13 Cooling fan drive motor 14 Nitrogen gas introduction valve 15 Gate valve

Claims (4)

[Claims] 1. A finely divided solder having a low degree of oxidation is dispersed in a dispersion medium containing an organic solvent as a main component and adjusted so that all of the dispersion medium evaporates at a soldering temperature in vacuum. Ink-like solder for printing characterized by 2. A method of soldering an electronic component on a holding substrate in a fine dimension, which is a dispersion medium containing an organic solvent as a main component and adjusted so that all of it is evaporated at a soldering temperature in vacuum. In the dispersion medium, using a printing ink-like solder in which fine solder powder having a low degree of oxidation is dispersed, a step of printing a solder pattern on the holding substrate, a step of mounting an electronic component on the solder pattern, and a vacuum. A fine soldering method comprising a step of heating and melting the solder pattern at a solder reflow temperature therein, and a step of cooling the solder pattern to fix the solder pattern and an electronic component therein. 3. The dispersion medium is prepared by adding one or more selected from resinous substances, higher alcohols and activator components to an organic solvent. Ink-like solder for printing and fine soldering method described in the above. 4. The printing ink-like solder and fine soldering method according to claim 1, wherein the dispersion medium is adjusted so as to evaporate at a temperature of 50 to 250 ° C. in a vacuum having a pressure of 1 mmHg or less. ..