Surface treatments for contact pads used in semiconductor chip packagages and methods of providing such surface treatments
An inorganic solder mask ( 48 ) for use as a surface treatment in masking a connection conductor ( 32 ) of a semiconductor chip package ( 10 ) against solder wetting when mounting the chip package ( 10 ) to a printed wiring board ( 50 ) or other substrate. The connection conductor ( 32 ) is partially covered by a metallization contact ( 42 ) formed from a distinct metal. The inorganic solder mask ( 46 ) is applied to an exposed portion ( 44 ) of the connection conductor ( 32 ) not covered by the metallization contact ( 42 ). The metallization contact ( 42 ) is not coated by the inorganic solder mask ( 46 ). The presence of the inorganic solder mask ( 46 ) significantly reduces or prevents wetting of the exposed portion ( 44 ) when molten solder is present on the connection conductor ( 32 ) without affecting the solidified solder layer ( 48 ) formed on the metallization contact ( 42 ). As a result, an extraneous mass of solder does not solidify on the exposed portion ( 44 ) of the connection conductor ( 32 ).
1. A semiconductor package for mounting onto a substrate, comprising:
a semiconductor chip;
a molding compound surrounding the semiconductor chip;
a carrier attached to the semiconductor chip, the carrier including a connection conductor with a contact pad carrying a metallization contact composed of a first conductor and an exposed region composed of a second conductor adjacent to said metallization contact, wherein the exposed region is recessed relative to the contact pad to lie in a different horizontal plane than the contact pad; and
an inorganic masking layer on said exposed region of said connection conductor, said inorganic masking layer operating to significantly reduce wetting of said exposed portion by molten solder that, upon solidification, forms a solder layer on said metallization contact.
2. The semiconductor package of claim 1 , wherein said first conductor comprises a metal, and said inorganic masking layer comprises a conversion coating.
3. The semiconductor package of claim 2 , wherein said conversion coating is selected from the group consisting of a molybdate conversion coating, a sulphite/oxalate conversion coating, and a persulphate conversion coating.
4. The semiconductor package of claim 1 , wherein said second conductor comprises nickel, molybdenum, or titanium, and said first conductor comprises gold or palladium-gold.
5. The semiconductor package of claim 1 , wherein said metallization contact has an outer perimeter, and further comprising:
a solder layer coating said metallization contact, said solder layer confined substantially within said outer perimeter of said metallization contact.
6. The semiconductor package of claim 1 , wherein the masking layer is only applied to the exposed region of the connection conductor.
7. The semiconductor package of claim 1 , wherein the carrier comprises a stack of patterned metal layers, wherein the stack of patterned metal layers are sectioned into a number of mutually-isolated connection conductors having side edges that are mutually isolated by apertures, and wherein the number of mutually-isolated connection conductors includes the connection conductor.
8. The semiconductor package of claim 1 , wherein the semiconductor chip includes connection regions, wherein the semiconductor chip is attached to the connection conductor by a conductive adhesive layer, and wherein each of the connection regions is electrically coupled with a bond pad on another connection conductor by a bonding wire.
9. A method for attaching the semiconductor chip package of claim 1 to a substrate comprising:
supplying molten solder on the metallization contact;
preventing solder wetting of the exposed region of the connection conductor with the inorganic masking layer; and
attaching the semiconductor chip package to the substrate by allowing the molten solder to solidify to form a solder layer on the metallization contact for establishing an electrical connection between the metallization contact and a contact pad on the substrate.
10. The method of claim 9 , wherein the inorganic masking layer further comprises a conversion coating, and masking the exposed region further comprises:
forming a conversion coating on the exposed region of the connection conductor of the semiconductor chip package.
11. The method of claim 10 , wherein the conversion coating is selected from the group consisting of a molybdate conversion coating, a sulphite/oxalate conversion coating, and a persulphate conversion coating.
12. The method of claim 9 , wherein the exposed region of the connection conductor comprises nickel, molybdenum, or titanium, and the metallization contact comprises gold or gold-palladium that is applied on the exposed region of the connection conductor.
13. The method of claim 9 , wherein the masking layer is only applied to the exposed region of the connection conductor.
14. The semiconductor package of claim 1 , wherein the exposed region is a surface region of a metal layer and wherein the contact pad is attached to the metal layer via a patterned metal layer.
15. The semiconductor package of claim 1 , wherein the exposed region is a surface region of a metal layer and wherein the contact pad is attached to the metal layer via a second metal layer and a patterned metal layer.
16. The semiconductor package of claim 1 , wherein said second conductor comprises nickel, molybdenum, or titanium and wherein the masking layer is only applied to the exposed region of the connection conductor.