JPS6054780B2 - Manufacturing method of circuit board for watches - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a circuit board for a timepiece, in which an IC wirelessly bonded to a flexible printed board is encapsulated and molded with a thermoplastic resin.

Conventionally, thermosetting resins have been used as encapsulating resins for ICs, and there have been no examples of thermoplastic resins.

Most of the thermosetting resins are epoxy resins, and the low-pressure encapsulation method using a transfer molding machine is used as the encapsulation method by molding. In the case of low-pressure encapsulation molding using the transfer molding machine, the molding time is long, about 1 and a half to 2 minutes.
This took several minutes and increased the number of man-hours. Possible methods for reducing the number of steps include further shortening the curing time of the epoxy molding material or using multiple molds. A fast-curing type with a faster curing time is currently under development, but even with the above-mentioned fast-curing type, the curing time takes about 1 minute, and the disadvantage is that it costs a lot of money when molding multiple molds. Ta. When inserting a flexible circuit board to which an IC is wirelessly bonded into a mold and encapsulating it using an IC encapsulation grade thermoplastic resin, the IC
If the substrate is left free without any restrictions as a mold, the substrate will be bent by the molding pressure, and the IC itself will be swept away by the flow during molding, making its position unstable.

Also, when the lead is bent by molding pressure, the lead may
A phenomenon of contact at the edge near the connection pad of C (shoulder touch) occurred, which was a fatal drawback for a watch. The present invention aims to solve the above-mentioned drawbacks and to provide an electronic timepiece that is inexpensive to manufacture, highly reliable, and small and thin. In order to achieve the above object, in the present invention, a wireless bonding (for example, minimod method) substrate is used as the IC mounting method, and a thermosetting resin is used as the IC encapsulating resin.
Using thermoplastic resin, which has excellent productivity, we can simultaneously encapsulate the IC and integrally mold the housing for other elements.

During molding, to prevent the IC from being washed away by the resin, the IC is held between the protrusions provided at the top and bottom of the mold.One protrusion is used to hold the bonding part on the wiring pattern side of the IC, and the other protrusion is used to hold the IC. The protrusion receives the back surface of the IC on the opposite side to the wiring pattern. In particular, the protrusion that receives the back surface of the IC is different from the other protrusion in that a spring material is provided at the lower part of the protrusion so that it can move up and down. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a plan view of a circuit board for a timepiece according to the present invention, and FIG. 2 is a plan view of a module for a digital electronic timepiece in which a display cell, a battery, a connector, etc. are incorporated into the circuit board for a timepiece shown in FIG. -A sectional view, Figure 3 is a side view illustrating the occurrence of shoulder touch when the lead is bent by molding pressure, and Figure 4 is a mold and flexible printed circuit board when the flexible printed circuit board is inserted into the mold. Figure 5 is a cross-sectional view showing a state in which the molded product is potted into a recess on the wiring pattern side of the IC after insert molding, and Figure 6 is another embodiment in which plastic is inserted into the recess. FIG. 7 is a cross-sectional view showing a state in which the molded products are fitted together, and FIG. 7 is a cross-sectional view showing another embodiment of the IC holding method. In Figs. 1 and 2, 1 is a flexible printed circuit board 3 on which an IC 2 is mounted using the minimod method, and is inserted into a molding die using a thermoplastic resin such as P that can be molded under low pressure.
OLYPHENYLENSULF[)E (PPS resin)
This is a circuit board for a watch which is encapsulated and molded using 1C encapsulation grade, and the circuit board for a watch 1 includes a connector storage part 4 for storing a connector serving as a connection with a display cell.
A battery storage section 5 for storing batteries, a crystal resonator storage section 6 for storing a crystal resonator, a step-up chip capacitor storage section 7 for storing a step-up chip capacitor, and other elements. The storage portions 8 and 9 are simultaneously molded.

The molding time is approximately 1 second, and productivity is excellent.Since the IC is bonded using the minimod method, the height of the IC mounting area is lower than when using wire. We were able to make the module thickness thinner than before.

Furthermore, the lead itself is stronger than the wire, and the bonding strength is also greater, so there is no disconnection or peeling, and reliability is improved. In addition, 10 is a sealing member, which will be described later. At this point, the recesses provided on the wiring pattern side of the IC are either filled with potting or fitted with plastic molded parts. Reference numeral 11 is a connector, 12 is a display cell, 13 is a battery, 14 is a boosting chip capacitor, and 15 is a battery connection spring mounted on the watch circuit board 1.

Electrical elements such as connectors, batteries, crystal oscillators, boosting chip capacitors, etc. are housed in each of the housing sections 4, 5, 6, 7, 8, and 9, and a display cell 12 is mounted thereon to form a module. Complete. This greatly reduced assembly man-hours. In FIG. 3, 16 is a lead for IC bonding in which the wiring pattern on the flexible printed board 3 extends to the device hole part, and B
2 shows a shoulder touch where the lead 16 comes into contact with the shoulder of the IC 2 due to the molding pressure.

As a means to eliminate the shoulder touch phenomenon, a flexible printed circuit board 3 is inserted into a molding die 17 as shown in FIG.
The bonding part 18 on the wiring pattern side of No. 2 is placed in the mold 1.
The lead part 16 is also received by the raised part 19 on the upper mold of the mold 7, and the lead part 16 is received by the raised part 20 of the lower mold of the molding die 17, opposite to the wiring pattern of the IC2. The convex portion 20 has a pin shape, and a spring 30 is provided at the bottom of the convex portion 20 to prevent the IC 2 from breaking by elastically holding the IC between the upper and lower molds. did. Also, the arrows in Figure 4 indicate the flow of thermoplastic resin.
By pouring the thermoplastic resin in this way, the IC 2 and the lead part 16 are molded so as to be pressed against the protrusion part 19 on the upper part of the mold 17, so the lead part 16 is not bent and the shoulder touch is perfect. It disappeared. Furthermore, when the thermoplastic resin was poured, IC2 was elastically held by the upper and lower protrusions 19 and 20, so that C2 did not move. In addition, there were concerns about the reliability of the processed product by receiving the wiring pattern side of IC2 with a mold, but this was a problem because only the bonding part 18 of IC2 was received, and the wiring pattern itself was not received. There was no.

Figure 4 shows the state in which the flexible printed circuit board 3 is inserted into the mold 17 and the mold 17 is closed.In this state, a molded product obtained by molding ■C-encapsulated grade of PPS resin at low pressure is shown. This is shown by the shaded area 40 in FIG. The potting section 21 protects the IC 2 and improves reliability. FIG. 6 shows a state in which a plastic molded product 22 is pushed into the recess instead of the potting described above.

Next, as another example of the method of receiving the wiring pattern part of C2, the wiring pattern side is also received by the pin 23.
Shown in the figure.

In this case, since it is received by the pin 23, the processing for forming the protrusion is easier than the protrusion 19, and since the encapsulated PPS resin flows between the pins as an IC, the pin 23 is supported.
3 is covered except for the bonding portion 18 of the lead 16 and the portion 24 in contact therewith, so that reliability can be maintained without potting or embedding a molded product later. As described above, the present invention provides protrusions on the upper and lower sides of the molding die when using IC encapsulating grade thermoplastic resin to encapsulate wirelessly bonded ICs and forming the housing portion of each element. The upper part should receive the bonding part on the wiring pattern side of the IC, and the other protrusion, which has a pin shape that can move up and down, should receive the back side of the IC, which is the opposite side to the wiring pattern of ■C. This eliminates the shoulder touch phenomenon, making it possible to create an electronic timepiece that is less expensive, thinner, more compact, and has significantly improved reliability.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a circuit board for a watch according to the present invention, and FIG.
The figure is an A-A cross-sectional view of an electronic watch module in which elements are incorporated into the circuit board shown in Figure 1, Figure 3 is a side view of the IC bonding part, and Figures 4 and 7 are diagrams of the IC and the IC in insert molding. 5 and 6 are cross-sectional views showing the molding die and the flow of resin, and FIGS. 5 and 6 are cross-sectional views of the IC mounting portion in the circuit board for a timepiece. 1...Circuit board for watch, 2...ICl
3...Flexible printed circuit board, 12...
...Display cell, 13...Battery.

Claims (1)

[Claims] 1. When molding a circuit board for a watch by insert molding a flexible printed board with an IC wirelessly bonded using thermoplastic resin, the bonding portion of the IC is held between the protrusions provided on the upper die of the molding die, and the lower A method for manufacturing a circuit board for a timepiece, characterized in that the back surface of the IC is elastically received by another vertically movable protrusion provided on the mold and the thermoplastic resin is encapsulated therein.