JP2000216300A - Manufacture of resin-sealing type printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method, wherein dielectric strength and adhesive strength with high reliability are secured where after an electronic component is soldered to a printed board, they are resin-sealed while flux residue is left as is without cleaning. SOLUTION: In a method for manufacturing a resin-sealing type printed circuit board, wherein an electronic part is mounted on a printed board by soldering, and their surrounding area is resin-sealed, the electronic part is, in a soldering process for the electronic component, reflow-soldered onto the printed board (a glass epoxy laminated board is suitable) with the use of cream solder comprising epoxy flux, wherein comprising epoxy resin as the main component, dicarboxylic acid (activator) is compounded with it, then the surrounding region of the printed board and the electronic part is sealed with epoxy resin, while flux residue left as is without being cleaned. Thereby excess dicarboxylic acid remaining in the flux residue is consumed by reacting it with a sealing resin (the epoxy resin), so that there is no need for cleaning the flux residue.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a resin-sealed printed circuit board.

[0002]

2. Description of the Related Art First, an assembly structure of a resin-sealed printed circuit board to which the present invention is applied will be described with reference to FIG. In the figure, 1 is a printed circuit board (a conductor pattern is formed on a main surface of an insulating substrate), 2 is an electronic component such as a semiconductor chip, 3 is a solder for electronically bonding the electronic component 2 to the printed circuit board 1, and 4 is a seal. Resin.

Here, in the conventional manufacturing method, a paste obtained by adding a rosin-based flux (a resin obtained by adding a solvent such as an alcohol, a halogen salt as an activator, and a thixotropic agent to rosin) to solder powder is used as the solder 3. After the cream solder is adopted, the cream solder is printed on the component mounting position of the printed circuit board 1 and the electronic component 2 is mounted, and then the electronic component 2 is carried into a reflow furnace and reflow soldering is performed. Next, the printed circuit board 1 on which the components are mounted is transferred to a cleaning step, and a rosin-based flux residue remaining on the surface of the solder 3 in the soldering step is cleaned with an organic solvent. Thereafter, the printed circuit board 1 is transferred to a resin sealing step, and the peripheral areas of the printed circuit board 1 and the electronic components 2 are sealed with a sealing resin (for example, epoxy resin) 4 by a mold forming method to form a resin-sealed printed circuit board. Complete.

[0004]

As described above, when the electronic component 2 is soldered to the printed circuit board 1 using a rosin flux as the solder flux, the solder 3
Excess rosin flux residue remains on the surface. Here, the printed circuit board 1 is kept without cleaning the flux residue.
When the resin is sealed with a resin, the flux residue inhibits the adhesiveness to the sealing resin 4 in a state after the resin sealing, so that not only a sufficient adhesive strength cannot be ensured, but also an adverse effect on electrical insulation. Will be exerted.

[0005] That is, FIG. 3 shows the adhesion amount of rosin-based flux residue and the bonding strength of the sealing resin (tensile shear bonding strength).
FIG. 4 is a graph showing the relationship between the adhesion amount of rosin-based flux residue and the AC withstand voltage (dielectric breakdown voltage). As can be seen from FIGS. If the amount exceeds 0.1 mg / cm ² , the adhesive strength and the AC withstand voltage rapidly decrease.

Therefore, conventionally, the printed circuit board 1 is washed after the electronic components 2 are soldered, and the quality is ensured by controlling the residual amount of the flux residue to be 0.1 mg / cm ² or less. However, incorporating a cleaning process into the component mounting line of a printed circuit board increases the cost of the assembly process, and may reduce the reliability of the product depending on variations in cleaning.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve the above-mentioned problems. An object of the present invention is to provide a method for manufacturing a resin-sealed printed circuit board improved so as to ensure high adhesive strength and dielectric strength.

[0008]

According to the present invention, there is provided, in accordance with the present invention, a resin-sealed print in which electronic components are mounted on a printed circuit board, soldered and mounted, and the periphery thereof is sealed with a resin. In a method of manufacturing a circuit board, in a soldering step of an electronic component, the electronic component is reflow-soldered to a printed circuit board using a cream solder containing an epoxy resin as a main component and an epoxy resin flux to which an activator is added, and a flux residue. Is sealed with epoxy resin without cleaning (claim 1), and is specifically realized in the following manner.

(1) As an activator of Epoxy flux,
Dicarboxylic acid used as a curing agent for epoxy resin is blended (claim 2). (2) A glass epoxy laminate is used as a printed circuit board (claim 3).

In the above method, the reaction temperature of the epoxy flux is lower than the melting temperature of the solder, and in the reflow soldering step of the electronic component, the reaction of the epoxy flux starts first before the solder is melted, and the activator dicarboxylic acid is used. Acid cleans the solder joints. Subsequently, the solder is melted by an increase in the heating temperature, and the electronic component and the conductor pattern on the printed board are soldered. During this time, the reaction of the epoxy resin proceeds, and the epoxy resin, which is the main component of the epoxy resin, proceeds with the curing reaction with the dicarboxylic acid (which is also a curing agent for the epoxy resin) as the activator. The reaction is almost completed, and the cured epoxy resin covers the soldered portion and reinforces the joint. In the state after the reflow soldering, a residue of the epoxy resin containing an excess of dicarboxylic acid remains at a soldering portion on the printed circuit board.

Then, the peripheral area of the printed circuit board is sealed with an epoxy resin without cleaning, and the excess dicarboxylic acid (activator) contained in the flux residue and the epoxy resin as the sealing resin undergo a curing reaction. However, dicarboxylic acid is almost consumed by this curing reaction, and the corrosiveness of the dicarboxylic acid is reduced, and the epoxy resin, which is a main component of epoxy resin, and the epoxy resin of the sealing resin are firmly adhered to each other. Also, in this case, if a glass epoxy laminated substrate is employed as the printed circuit board, the epoxy resin component of the printed circuit board and the epoxy resin flux residue are firmly adhered to each other in the same manner as described above. As a result, the printed circuit board is not cleaned (no cleaning process is required)
Even in this state, a high adhesive strength can be secured between the residue of the epoxy resin, the sealing resin, and the printed circuit board, and the dielectric strength of the printed circuit board can be secured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a view showing a process of assembling a printed circuit board according to the present invention, and FIG. 2 is an assembly structure diagram of the printed circuit board.

That is, in this embodiment, a glass epoxy laminate is used as the printed board 1 and the solder 3 for electrically connecting the electronic component 2 to the board is used as the printed board 1.
A paste-like cream solder containing an epoxy resin containing an epoxy resin as a main component and a dicarboxylic acid as an activator is used, and after printing this cream solder on a printed circuit board 1, an electronic component 2 is mounted and reflow soldering is performed. Do. Next, without removing the flux residue
The printed circuit board is completed by sealing the peripheral areas of the printed circuit board 1 and the electronic component 2 with epoxy resin (sealing resin 4).

Here, the cream solder is, for example, an epoxy resin-based cream solder (for example, Sn63 / Pb37 cream) consisting of 79% of epoxy resin, 16% of dicarboxylic acid, and <5% of thixotropic agent. Solder Alph
a AP4000 (manufactured by Alpha Metal) shall be adopted.

When the adhesive strength of the sealing resin of the printed circuit board assembled by the method of the above embodiment was examined, the printed circuit board was compared with a conventional product in which rosin-based flux residues were washed after soldering and resin sealing was performed. It has been confirmed that the same adhesive strength can be secured. The printed circuit board assembled by the method of the embodiment and the conventional printed circuit board were used as test samples to verify the dielectric strength by a test.
As shown in the following table, the improvement of the dielectric strength was clearly confirmed.

[0016]

[Table 1]

[0017]

As described above, according to the manufacturing method of the present invention, in the process of assembling a printed circuit board, the step of cleaning flux residues after soldering and mounting electronic components can be omitted. Accordingly, assembling steps and costs can be reduced as compared with the conventional method.

[Brief description of the drawings]

FIG. 1 is an assembly process diagram of a printed circuit board according to an embodiment of the present invention.

FIG. 2 is a sectional view showing an assembly structure of a printed circuit board according to the manufacturing method of FIG. 1;

FIG. 3 is a diagram showing the relationship between the adhesion amount of a flux residue and the adhesive strength of a sealing resin in a conventional method using a rosin-based flux in a soldering step of an electronic component.

FIG. 4 is a diagram showing the relationship between the amount of adhered flux residue and the AC breakdown voltage of a printed circuit board in a conventional method using a rosin-based flux in a soldering step of an electronic component.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Electronic component 3 Solder 4 Sealing resin 5 Flux residue

Claims (3)

[Claims] In a method of manufacturing a resin-sealed printed circuit board in which an electronic component is mounted on a printed circuit board by soldering, and a peripheral area thereof is sealed with a resin, in the soldering step of the electronic component, epoxy resin is used. The electronic component is reflow-soldered to the printed circuit board using a cream solder containing an epoxy resin flux to which an activator is added as a main component, and then the printed circuit board and the electronic component are sealed with epoxy resin without cleaning the flux residue. A method for producing a resin-encapsulated printed circuit board, comprising: 2. The method according to claim 1, wherein a dicarboxylic acid is blended as an activator for epoxy resin. 3. The method according to claim 1, wherein a glass epoxy laminate is used as the printed circuit board.