Method for enhancing fatigue life of ball grid arrays
First Claim
1. A method for making solder electrical interconnections in an electronic component assembly comprising the steps of:
- applying a first solder having a first melting point to first pads on the surface of a first substrate of an electronic component assembly;
forming a solder structure comprising;
an inner core of a second solder having a second melting point which is higher than the melting point of the first solder to which the structure is to be bonded;
a layer of a metal wettable by the first solder and having a melting point higher than the second melting point of the second solder of the inner core;
an outer layer of a third solder having a third melting point which provides a wettable surface for attachment of the solder structure and passivates the layer of metal from oxidation and corrosion, the third melting point being lower than the second melting point;
bonding the solder structure to the first pad by reflowing the first and third solders;
applying a fourth solder to second pads on the surface of a second substrate of the electronic component assembly;
positioning the second pads on the surface of the second substrate electronic component assembly to be joined proximate to the corresponding solder structure containing pads on the first substrate;
heating the substrates to a temperature sufficient to form a bond between the solder structure and the pads of the second substrate; and
cooling the bonded interconnected assembly.
1 Assignment
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Accused Products
Abstract
This invention relates to a solder structure which provides enhanced fatigue life properties when used to bond substrates particularly at the second level such as BGA and CGA interconnections. The solder structure is preferably a sphere or column and has a metal layer wettable by solder and the structure is used to make solder connections in electronic components such as joining an electronic module such as a chip connected to a MLC which module is connected to a circuit board. The solder structure preferably has an overcoat of solder on the metal layer to provide a passivation coating to the metal layer to keep it clean from oxidation and corrosion and also provide a wettable surface for attachment of the solder structure to solder on the pads of the substrate being bonded.
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Citations
5 Claims
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1. A method for making solder electrical interconnections in an electronic component assembly comprising the steps of:
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applying a first solder having a first melting point to first pads on the surface of a first substrate of an electronic component assembly;
forming a solder structure comprising;
an inner core of a second solder having a second melting point which is higher than the melting point of the first solder to which the structure is to be bonded;
a layer of a metal wettable by the first solder and having a melting point higher than the second melting point of the second solder of the inner core;
an outer layer of a third solder having a third melting point which provides a wettable surface for attachment of the solder structure and passivates the layer of metal from oxidation and corrosion, the third melting point being lower than the second melting point;
bonding the solder structure to the first pad by reflowing the first and third solders;
applying a fourth solder to second pads on the surface of a second substrate of the electronic component assembly;
positioning the second pads on the surface of the second substrate electronic component assembly to be joined proximate to the corresponding solder structure containing pads on the first substrate;
heating the substrates to a temperature sufficient to form a bond between the solder structure and the pads of the second substrate; and
cooling the bonded interconnected assembly. - View Dependent Claims (2, 3, 4, 5)
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Specification