Electromagnetic shielding method and electromagnetic shielding film

1. An electromagnetic shielding method comprising the steps of:

disposing a flexible electromagnetic shielding film including a laminate of at least an insulating layer and a conductive metal layer to cover a portion to be electromagnetically shielded on a printed wiring board so that the insulating layer faces the printed wiring board, the conductive metal layer having a higher melting temperature than that of the insulating layer;

heating the electromagnetic shielding film to a temperature to melt and contract the insulating layer, thereby bonding the conductive metal layer to a grounding conductor of the printed wiring board and electrically connecting the conductive metal layer to the grounding conductor, the heating temperature being higher than the melting temperature of the insulating layer and lower than the melting temperature of the conductive metal layer; and

cutting an excess portion of the electromagnetic shielding film outside a bonded portion between the conductive metal layer and the grounding conductor.

2. The electromagnetic shielding method according to claim 1 ,

wherein the electromagnetic shielding film further includes a conductive adhesive layer provided between the insulating layer and the conductive metal layer, the melting temperature of the conductive adhesive layer being lower than that of the conductive metal layer;

the heating temperature of the electromagnetic shielding film is higher than the melting temperatures of the insulating layer and the conductive adhesive layer and lower than the melting temperature of the conductive metal layer; and

the conductive metal layer is bonded and electrically connected to the grounding conductor of the printed wiring board through the melted conductive adhesive layer.

3. The electromagnetic shielding method according to claim 1 ,

wherein the electromagnetic shielding film is heated while being pressure-bonded to the grounding conductor of the printed wiring board from the conductive metal layer side using a thermocompression bonding bar to melt and contract the insulating layer, thereby bonding the conductive metal layer to the grounding conductor.

4. The electromagnetic shielding method according to claim 1 ,

wherein the electromagnetic shielding film is heated while being pressure-bonded to the grounding conductor of the printed wiring board from the conductive metal layer side using a thermocompression bonding bar with a cutter to melt and contract the insulating layer, thereby bonding the conductive metal layer to the grounding conductor and cutting off the excess portion of the electromagnetic shielding film outside the bonded portion between the conductive metal layer and the grounding conductor.

5. The electromagnetic shielding method according to claim 1 ,

wherein a grounding conductor pattern is provided on the printed wiring board so as to surround the portion to be electromagnetically shielded; and

a current is passed through the grounding conductor pattern to melt and contract the insulating layer by Joule heat generated in the grounding conductor pattern, thereby bonding the conductive metal layer to the grounding conductor.

6. The electromagnetic shielding method according to claim 1 ,

wherein the electromagnetic shielding film is bonded to the printed wiring board to leave an unbonded portion; and

the unbonded portion is used as an opening through which air between the printed wiring board and the electromagnetic shielding film is sucked to close the opening by bonding.