Low cost flexible substrate
View Patent ↗A low cost flexible substrate is described which comprises a thin metal foil and a layer of solder mask. The metal foil layer is patterned to create tracks and lands for solder bonding and/or wirebonding and the layer of solder mask is patterned to create openings for solder bonding, wirebonding and/or for mounting the die. The substrate may be used as a package substrate to create a packaged die or may be used as a replacement for more expensive flexible printed circuit boards.
1. A method of packaging a die comprising:
bonding a die to a flexible substrate comprising a patterned metal foil layer and a patterned layer of solder mask, the solder mask comprising one of a liquid solder mask and a dry film solder mask; and
over molding the die and the flexible substrates;
wherein the die is attached to the patterned metal foil layer through an opening in the patterned layer of solder mask.
2. The method according to claim 1 , further comprising:
forming wirebonds between pads on the die and tracks formed in the patterned metal foil layer.
3. The method according to claim 1 , further comprising:
attaching a plurality solder balls to the flexible substrate, each solder ball being attached to the metal foil layer through an opening in the layer of solder mask; and
reflowing the solder balls.
4. The method according to claim 1 , wherein the solder mask comprises a dry film solder mask.
5. The method according to claim 4 , wherein the patterned layer of solder mask has a thickness selected from 20 μm, 25 μm, 30 μm and 35 μm.
6. The method according to claim 1 , wherein the solder mask comprises a liquid solder mask and the patterned layer of solder mask is approximately 25 μm thick.
7. The method according to claim 1 , further comprising repeating the method to form a multilayer substrate and forming vias in interior solder layers.
8. The method according to claim 1 , further comprising applying the solder mask layer to the metal foil layer and patterning the metal foil.