JPS621278B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method for leadless components soldered to a conductor pattern surface of a printed wiring board.
The purpose is to enable individual coating of leadless components on the printed wiring board.

In general, leadless components that are soldered to the conductor pattern surface of a printed wiring board have exposed parts and electrodes, and there is a risk of condensation or corrosion of the electrodes during use. If it is made of silver paint, there is a problem in that silver migrates during soldering. Therefore, in the printed wiring board on which the above-mentioned leadless components are mounted, it is necessary to form a resin protective film on the mounted leadless components. As methods for coating leadless components on such printed wiring boards with resin protective films, resin casting methods and spraying methods are known. However, in the above method, the leadless component and the conductor pattern surface of the printed wiring board are covered with resin at the same time, making it difficult to solder when replacing and wiring the leadless component. Ta.

The present invention eliminates such conventional drawbacks, and the present invention will be described below with reference to drawings of embodiments.

The drawing shows an embodiment of the coating method of the invention. First, as shown in FIG. 1, a leadless component is attached between the conductor layers 2, 2 of the printed wiring board 1. Here, the chip resistor 3 as a leadless component is attached by dip soldering or reflow soldering with its electrode portion 4 facing the conductor layers 2, 2, and is also used as a leadless component. The electrode portions of the chip-shaped transistor/IC/LSI 5 are attached to the conductive layers 2, 2 by a bonding method using wires 6. Next, the printed wiring board 1 on which the leadless components 3 and 5 are mounted is placed on a support stand of a screen printing machine with the component-attached surface facing upward, and the printing mask 7 is placed opposite the component-attached surface. let Here, the printing mask 7 is opposed to the component adhering surface of the printed wiring board 1 via a spacer 8 having the height of the leadless components 3 and 5 mounted on the printed wiring board 1, and the spacer 8 As a result, a gap 9 facing the printed wiring board 1 is formed. Further, the printing mask 7 is provided with stepped holes 10 facing the leadless components 3 and 5 mounted on the printed wiring board 1, respectively. next,
Resin paint 1 placed on the surface of the above printing mask 7
1 is three-dimensionally printed on the leadless parts 3 and 5 mounted on the printed wiring board 1 as shown in FIG. 2 by one printing operation of the squeegee 12. Thereafter, the printed wiring board 1 is coated with the three-dimensional resin paint 11 in a heated atmosphere, and as shown in FIG. A separate resin protective film 13 is formed.

Example A resin paint prepared by blending trimethanolamine as a curing agent with an epoxy resin and adding butyl acetate as a solvent to adjust the viscosity to 120 centipoise was used. A stainless steel plate with a thickness of 0.2 mm is used as a printing mask, and the step depth is 0.1 mm and the step width is 0.2 mm.A round stepped hole with a diameter of 5.0 mm is used for the chip capacitor, and a 5.0 mm diameter hole is used for the chip resistor. Square stepped holes of 2.5 mm were formed, and the resin paint remained on the steps during the first printing so that it could be added to the next print volume. A circular chip capacitor with a diameter of 4.0 mm and a thickness of 1.5 mm is placed on the conductor pattern side of the single-sided printed wiring board, and a 4.5 mm thick 1.5 mm
A 2.0mm square chip resistor was attached to each.
Furthermore, a spacer having the same height as the leadless component and with a corresponding portion of the leadless component as a blank hole was used, and was placed between the printed wiring board and the printed mask. Then, the above printing mask was used in place of the screen mask of the screen printing machine, and the squeegee was used as is to perform one printing operation in one direction at a speed of 10 cm per second. In this case, the first step is to apply resin paint on the top surface of the leadless component, the second step is to apply resin paint to the side surface of the leadless component, and the third step is to apply resin paint from the side surface of the leadless component around the connection area with the conductor shoulder of the printed wiring board. The chips were three-dimensionally printed across the entire area, and the average printing thickness on the top and side surfaces of the chip product was about 8 microns. and,
The printed film of this resin paint was cured at 150°C for 30 minutes to form a resin protective film. Note that if there is no step, printing of the resin on the side surface of the chip component is insufficient or impossible. In addition, without the spacer, resin would adhere to the underside of the printing mask, causing smearing or unnecessary spreading during subsequent resin printing.

In this way, it is possible to avoid problems such as breakage or falling off that would occur if bare leadless components that are not covered with a protective resin film are directly attached to a printed wiring board, and the protective resin film can be coated only where necessary. Printing can be done uniformly and quickly in one printing operation per year, which is advantageous in terms of economy and shortening of work.

Incidentally, as the resin paint, resin paints such as epoxy, melamine, acrylic, polyethylene, polyamide, and polyester can be used. When the electrode portion of a leadless component is formed of silver paint, it is preferable to use an epoxy resin containing tertiary amine as a curing agent as a base in order to prevent silver migration. In addition, resins such as polyester, epoxy, acrylic, and polyurethane that are UV-curable by adding a photoinitiator can be used.

As described above, the present invention has the advantage that resin paint can be individually and three-dimensionally printed on chip parts by one printing operation.

[Brief explanation of the drawing]

The drawings show one embodiment of the coating method of the present invention, FIGS. 1 and 2 are diagrams for explaining the three-dimensional printing process of resin paint in the same method, and FIG. 3 shows the curing process of resin paint in the same method. FIG. 1...Printed wiring board, 2...Conductor layer, 3, 5...
Leadless parts, 4... Electrode section, 7... Printing mask, 8... Spacer, 9... Gap, 10... Stepped hole, 11... Resin paint, 12... Squeegee, 13... Resin protective film .

Claims (1)

[Claims] 1 Attach leadless components to appropriate locations on the conductor pattern surface of the printed wiring board, and install a printed mask having stepped holes on the component mounting surface of the printed wiring board at locations corresponding to the leadless components attached to the printed wiring board. The resin paint placed on the printing mask surface is printed so as to individually cover the leadless components on the printed wiring board by printing with a squeegee, facing each other using a spacer having the same thickness as the leadless components, A method for coating a leadless component mounted on a printed wiring board, characterized in that the resin paint is then cured to form a resin protective film for the leadless component.