JP2793737B2 - Manufacturing method of precoated substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for manufacturing a precoated substrate. More specifically, the present invention relates to a method for manufacturing a pre-coated substrate that can efficiently remove a flux residue, a solder ball, and the like after solder coating.

[0002]

2. Description of the Related Art As a method of manufacturing a pre-coated board in which solder is coated on a pad of a printed wiring board, a cream solder is applied to the pad of the printed wiring board and heated in a reflow furnace such as a normal hot air furnace or an infrared furnace. And the pad is coated with solder (hereinafter, also referred to as pre-coat).

In the above method, the cream solder is mainly composed of solder particles and a flux, and the flux generally contains a solvent for adjusting the viscosity.

In recent years, when the pitch between pads is small and it is difficult to print cream solder on each pad in the above-mentioned method of manufacturing a precoated substrate, a cream solder in which solder particles are diluted with flux is used. A method has been proposed in which solder is solid printed on a pad and reflowed. That is, by using the cream solder diluted with the flux, the solder is selectively coated on the pad after reflow due to the adhesion of the solder to the pad and the surface tension.

However, in the above-described method in which the amount of flux is large by diluting the solder with the flux, after the reflow, a large amount of flux residue that has performed its function adheres to the substrate surface. Such a flux residue contains a metal salt of an organic acid, a halide, or the like, and causes migration or corrosion of metal ions. Further, the solder microspheres generated during the reflow and existing in the flux residue cause a short circuit between the pads.

For this reason, in a printed wiring board that requires long-term reliability, it is necessary to remove flux residues and solder microspheres.

Conventionally, the removal of flux residue and solder microspheres after reflow is mainly performed by removing the printed circuit board from a reflow furnace and then cleaning the printed circuit board with an organic solvent capable of dissolving the flux residue. Had been implemented.

[0008]

However, when the above-mentioned method for removing the flux residue is applied to the above-mentioned method for producing a pre-coated substrate having a very large amount of flux residue, treatment with an organic solvent in which the flux residue is dissolved, that is, There is a problem that the amount of waste organic solvent waste liquid in purification by distillation and distillation is increased, resulting in a heavy burden in terms of process and cost.

Attempts have also been made to use water-soluble flux as a residue after reflowing, but at present it is not possible to avoid the problem of waste treatment of flux residue.

[0010]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems in the method of manufacturing a precoated substrate. As a result, after reflow of the solder paste, before the flux residue is solidified by this <br/> and to shower cleaning or spray cleaning the substrate with perfluorinated organic liquid, surprisingly, flux residues adhering to the substrate And the solder microspheres are removed very well, and the subsequent cleaning with an organic solvent can be significantly reduced, or in some cases, the cleaning with the organic solvent can be unnecessary,
The present inventors have found that the flux residue is substantially insoluble in the inert organic liquid at room temperature and can be easily removed from the perfluoro organic liquid by means such as filtration, thereby completing the present invention.

According to the present invention, the cream solder applied on the pad of the printed wiring board is heated in a heating vapor of a perfluoro organic liquid, and after the solder is reflowed, before the flux residue of the cream solder solidifies, The substrate is shower-washed or spray-washed with a liquid perfluoro organic liquid heated to a temperature equal to or higher than the melting point of the flux residue .
A pre-coat the substrate manufacturing method characterized by that.

In the present invention, the printed wiring board has a pad portion for soldering in the wiring pattern.
Any material can be used without particular limitation as long as it has resistance under heating conditions in reflow. For example, a glass substrate
Epoxy resin laminate, glass substrate-polyimide resin laminate, glass substrate-BT (bismaleide-triazine) resin resin laminate, synthetic resin substrate such as composite resin substrate, flexible substrate such as polyimide resin, polyester resin, aluminum, A wiring pattern formed by a conductive layer made of copper, nickel, aluminum, etc. on an insulating substrate such as an insulated metal-based insulating substrate obtained by coating a metal plate such as iron or stainless steel with a thermosetting resin such as epoxy resin. Is mentioned.

In the present invention, as the cream solder, a known solder containing a flux is used without any particular limitation. In general, a composition mainly containing components including solder alloy particles and flux and, if necessary, an organic solvent is generally used. As the flux, one having a melting point lower than that of solder, specifically, rosin or a derivative thereof is generally used.

The ratio of the flux and the solder particles in the cream solder is appropriately determined according to the pitch of the pad so that the solder concentration at which the solder can be divided and coated on the pad after reflow. For example, when the pad pitch is 0.3 mm or less, generally, the flux 10
It is preferable that the composition comprises 50 to 50% by weight and 90 to 50% by weight of solder alloy particles, and if necessary, other additives such as a solvent. In the above composition, an embodiment to which the present invention is effectively applied is a case where the flux ratio is 15% by weight or more, particularly 25% by weight or more.

In the present invention, the application of the cream solder to the pad is not particularly limited, but a method of solid printing in a range where the pad exists is preferable. As the printing method, a known printing method using a metal mask and a screen mesh plate is employed without any particular limitation.

In the present invention, a known method of reflowing the cream solder printed on the pad is not particularly limited. Among them, a method capable of performing reflow under an inert atmosphere having an oxygen concentration of 0.02% by volume or less, particularly, prints cream solder over the entire pad row and generates a solder bridge between the pads when reflow is performed. It is preferable that the pre-coating can be performed uniformly on the pad without using such a method. Examples of such a reflow method include a heating furnace such as a perfluoro organic liquid steam heating furnace and an infrared heating furnace maintained in an inert gas atmosphere such as nitrogen. ,
A method of heating to a temperature equal to or higher than the melting point of the solder may be used.

That is, the present inventors have proposed a method in which cream solder diluted with a flux is solid-printed in a region where a pad is present, and the individual pad is selectively coated with solder during reflow. Research was conducted to improve the ease of selective coating (hereinafter, also referred to as selective coating properties). As a result, the selective coatability is significantly impaired by the decrease in fluidity due to oxidation of the solder surface during melting, and even when using cream solder diluted with a large amount of flux, the occurrence of solder bridges between pads,
It was found that the amount of solder on the pad varies. Based on such knowledge, the above phenomenon could be prevented by performing the reflow of the cream solder diluted with the flux under the above-mentioned inert atmosphere.

In the reflow method under an inert atmosphere,
In particular, a method of performing reflow using a vapor of a perfluoro organic liquid is remarkable, since the effect of preventing the occurrence of solder bridges between pads and the effect of preventing a variation in the amount of solder on the pads are remarkable. According to the reflow method using the perfluoro organic liquid, the pitch of the pad is 0.2 m
m, and further, it is sufficiently applicable to a printed wiring board of 0.1 mm, and it is possible to accurately manufacture a fine precoated substrate.

Known perfluoro organic liquids are used without particular limitation. For example, perfluoro hydrocarbon, perfluoropolyether, perfluorotrialkylamine and the like can be mentioned.

In the above method, in particular, in the method of reflowing with the vapor of a perfluoro organic liquid, the perfluoro organic liquid of the vapor source can be commonly used as a cleaning liquid as the perfluoro organic liquid used for cleaning described later. Since the purification process can be simplified and the cleaning can be performed in the vapor phase, there is no need to separately provide a means for preventing vapor leakage, which is extremely advantageous.

A feature of the present invention is that, after reflowing the cream solder, before the flux residue solidifies, the substrate is shower-washed or spray-washed with a liquid of a perfluoro organic liquid heated to a temperature not lower than the melting point of the flux residue. It is in.

That is, the present inventors have repeatedly studied an efficient cleaning method for reducing the cleaning of the flux residue with a soluble organic solvent. As a result, a perfluoro organic liquid having a low solubility of the flux residue was used. Even if you do
As described above, it has been found that a surprising cleaning effect is exhibited by selecting the cleaning timing and the cleaning conditions.

Therefore, after the solder paste is reflowed and the flux residue is solidified and then washed with the above-mentioned inert organic liquid, or a liquid of a perfluoro organic liquid heated to a temperature lower than the melting point of the flux residue. When the substrate is cleaned by the method described above, the effects of the present invention cannot be achieved.

In the present invention, known perfluoro organic liquids are used without particular limitation. Typical examples include organic liquids in which most of the hydrogen in the molecule has been replaced by fluorine, specifically, perfluoro hydrocarbons, perfluoropolyethers, perfluorotrialkylamines, and the like. A liquid having a boiling point higher than the melting point of the flux residue may be appropriately selected and used from the above-mentioned perfluoro organic liquids. When the perfluoro organic liquid is used for reflow of the solder by steam, a perfluoro organic liquid having a boiling point higher by about 30 ° C. than the melting point of the solder may be selected and used.

In the present invention, the cleaning method includes a method of showering a liquid perfluoro organic liquid on the substrate surface,
Laying method is adopted. Further, the liquid pressure at the time of cleaning may be within a range in which the solder does not peel off. Generally, when the above-mentioned cleaning is performed at a temperature lower than the melting point of the solder and higher than the melting point of the flux residue, it is preferable to apply a perfluoro organic liquid within a range of 5 kg / cm ² or less. In addition, in the case where the temperature is higher than the melting point of the solder, the perfluoro organic liquid is 3
It is preferable to act within a range of kg / cm ² or less.

In the present invention, the cleaning of the flux residue by the inert solvent is performed by reflowing the cream solder.
The method is not particularly limited as long as it is performed before the flux residue is solidified. However, it is preferable to perform the process immediately after reflowing the solder in order to further improve the cleaning effect. Therefore, it is preferable to carry out in the reflow furnace.

FIG. 1 is a conceptual diagram showing one embodiment of an apparatus for manufacturing a precoated substrate used in the method of the present invention. The apparatus shown in FIG. 1 is a schematic diagram showing one embodiment of an apparatus for performing the method of the present invention. In the embodiment of FIG. 1, a cleaning apparatus 2 using a liquid perfluoro organic liquid is combined with a vapor heating furnace 1 for a perfluoro organic liquid. The steam heating furnace 1 includes a steam generation tank 3 having a perfluoro organic liquid storage tank 4 provided with a heater 5 at the bottom, a conveying means 6 for conveying and discharging a printed circuit board to and from the steam generation tank 3, and a steam generation tank 3. the outlet side, the shower perfluoro organic liquid of the liquid
Cleaning device 2 with nozzle for spraying or spraying
It is basically composed of The cleaning area by the above-described cleaning apparatus is formed so that the perfluoro organic liquid can be sprayed on the printed wiring board after the reflow before the flux residue solidifies. In general, there may be mentioned an embodiment provided immediately after the reflow zone of the generating tank, and an embodiment provided separately from the reflow zone while maintaining the temperature at or above the melting point of the flux residue. Further, in the cleaning apparatus, a heater 12 is provided in a perfluoro organic liquid storage tank 11 in order to keep the cleaning area at a constant temperature.
And heating. In this case, the storage tank and the heater can be shared with the above-mentioned steam generation tank. A cooling device 7 and an exhaust duct 8 are provided at the entrance and exit of the device in order to prevent leakage of steam.

The printed wiring board on which the cream solder has been applied on the pads is transported into the steam generating tank 3 by transport means 6 such as a belt conveyor, where the solder is reflowed and transported in the exit direction. After reflowing the solder,
Before the flux residue of the cream solder solidifies, the liquid perfluoro organic liquid heated to a temperature not lower than the melting point of the flux residue is showered from the nozzle 13 of the cleaning device 2.
The substrate is cleaned by spraying or spraying .

After the above-mentioned washing, it is preferable to incline the conveying means toward the outlet, for example, a belt conveyor or the like, because the perfluoro organic liquid can be desirably drained from the substrate. Further, the perfluoro organic liquid in the perfluoro organic liquid storage tank 4 is intermittently or continuously withdrawn at a time when the flux increased by washing, and loose substances such as fine solder balls reach a certain concentration, and after cooling as necessary. After removing the free matter with the filter 10, the mixture is preheated and supplied to the washing tank. In addition, if necessary, a part is collected in the collection tank 9.
And then to the above-mentioned generating tank.

The above-mentioned filter is not particularly limited as long as it has a function of removing free matter, but a layer capable of adsorbing and removing a small amount of dissolved flux residue such as a layer made of activated alumina or activated carbon particles. Are preferably provided alone or in several stages.

The perfluoro organic liquid extracted from the steam generation tank is also purified by a filter in the same manner as the above-mentioned washing liquid.
It is common to use them cyclically.

After the method of the present invention is performed on a printed wiring board, cleaning with a known flux residue-soluble solvent (including water) is not particularly limited.

[0033]

As will be understood from the above description, according to the method of the present invention, it is possible to obtain a precoated substrate from which flux residues have been efficiently removed.

Accordingly, the amount of the solvent used for cleaning the flux residue after the solder reflow can be reduced, and the trouble of the waste liquid treatment of the solvent can be remarkably reduced. In some cases, such a cleaning process can be omitted.

Further, there is an advantage that purification of the perfluoro organic liquid after washing the flux residue can be easily performed by filtration.

[0036]

EXAMPLES The present invention will be described below in more detail with reference to Examples, but it should be understood that the present invention is by no means restricted to such specific Examples.

Example 1 A pad having a width of 0.15 mm and a length of 3.0 mm was inserted into a pad of 0.3 mm.
Using a printed wiring board having four pad rows with 144 pitches, a mesh screen of 80 mesh and 130 μm thick cream solder (eutectic, flux content 25% by weight) over the entire area where the pads exist. Solid printing was performed using the plate.

Next, the printed wiring board was supplied to a vapor phase soldering tank (hereinafter, referred to as VPS) shown in FIG. V
In PS, as a vapor source, a perfluoro organic liquid having a boiling point of 216 ° C. (Perflud IL-310, trade name:
Tokuyama Soda Co., Ltd.) was used. After the reflow was completed, before the flux residue was solidified, the perfluoro organic liquid preheated to 200 ° C. was showered at a pressure of ² kg / cm ² at a rate of 6 L / min to wash the substrate.

After cleaning, the substrate was observed. As a result, most of the residual flux was removed (residual rate: 8%), and no fine solder balls were present.

No bridging occurred between the pads, and the variation in the amount of solder on the pads was found to be ± 25% or less as a result of measurement by a cross-sectional photograph.

COMPARATIVE EXAMPLE 1 In Example 1, after the reflow, the printed wiring board was taken out without washing with the perfluoro organic liquid, and as a result, the solid content of the flux residue containing the solder fine particles up to the solder level was found between the pads. Minutes remained.

COMPARATIVE EXAMPLE 2 In Comparative Example 1, the printed wiring board taken out of the VPS was showered at a pressure of ² kg / cm ² at a rate of 6 liters / minute with the perfluoro organic liquid preheated to 200 ° C. The substrate was washed.

After the cleaning, the substrate was observed. As a result, 63% of the residual flux remained.

Example 2 A pad having a width of 0.05 mm and a length of 2.2 mm was adjusted to 0.1 mm.
Using a printed wiring board having four pad rows having 400 pads at a pitch, a mesh screen of 150 mesh and 120 μm thick cream solder (eutectic, flux content 40% by weight) over the entire area where the pads exist. Solid printing was performed using the plate. Next, the printed wiring board was placed in a vapor phase soldering bath (hereinafter referred to as V
PS). In the VPS, a perfluoro organic liquid having a boiling point of 218 ° C. (Perflud IL-310, trade name: manufactured by Tokuyama Soda Co., Ltd.) was used as a vapor source. After the reflow, before the flux residue solidifies, the perfluoro organic liquid preheated to 200 ° C.
The substrate was washed by showering at a pressure of kg / cm ² at a rate of 6 l / min.

After cleaning, the substrate was observed. As a result, most of the residual flux was removed (residual rate: 15%), and no fine solder balls were present.

Further, before and after the removal of the flux residue, no bridge was generated between the pads, and the variation in the amount of solder on the pads was found to be ± 33% or less as a result of measurement by a cross-sectional photograph.

Example 3 A pad having a width of 0.10 mm and a length of 3.0 mm was applied to a pad of 0.1 mm.
Using a printed wiring board having four pad rows having 200 pads at a pitch, a cream screen (eutectic, flux content 35% by weight) of 100 mesh and 130 μm thickness is applied to the entire area where the pads are present. Solid printing was performed using the plate. Next, the printed wiring board was placed in a vapor phase soldering bath (hereinafter referred to as V
PS). In the VPS, a perfluoro organic liquid having a boiling point of 218 ° C. (Perflud IL-310, trade name: manufactured by Tokuyama Soda Co., Ltd.) was used as a vapor source. After the reflow, before the flux residue solidifies, the perfluoro organic liquid preheated to 200 ° C.
The substrate was washed by showering at a pressure of kg / cm ² at a rate of 6 l / min.

After cleaning, the substrate was observed. As a result, most of the residual flux was removed (residual rate: 12%), and no fine solder balls were present.

Further, before and after the removal of the flux residue, no bridge was generated between the pads, and the variation in the amount of solder on the pads was less than ± 22% as a result of measurement by a cross-sectional photograph.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of an apparatus for performing the method of the present invention. DESCRIPTION OF SYMBOLS 1 Steam heating furnace 2 Cleaning device 3 Steam generation tank 4 Storage tank 5 Heater 6 Conveying means 7 Cooling device 8 Exhaust duct 9 Recovery tank 10 Filter 11 Storage tank 12 Heater 13 Nozzle

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) H05K 3/10-3 / 26,3 / 34,3 / 38 C11D 7/30 B23K 1/00

Claims (1)

(57) [Claims] 1. A method of heating a solder paste applied on a pad of a printed wiring board in a heating vapor of a perfluoro organic liquid to reflow the solder, and before the flux residue of the cream solder solidifies, Cleaning the substrate with a liquid perfluoro organic liquid heated to a temperature equal to or higher than the melting point of the substrate by shower cleaning or spray cleaning .