Solder transfer sheet, solder bump, and solder precoating method using solder transfer sheet
Provided is a solder transfer sheet which is capable of increasing the amount of solder to be transferred without the occurrence of bridging. A solder transfer sheet 1 A includes a base material 5 , an adhesive layer 4 formed on the surface of the base material 5 , a solder powder-containing adhesive layer 3 formed on the surface of the adhesive layer 4 , and a solder powder layer 2 formed on the surface of the solder powder-containing adhesive layer 3 . In the solder powder layer 2 , particles of solder powder 20 are arranged in a one-layer sheet form. In the solder powder-containing adhesive layer 3 , solder powder 30 and an adhesive component 31 are mixed so as to have such a thickness that two or more layers of the solder powder 30 are stacked.
1. A solder transfer sheet comprising:
a base material;
an adhesive layer formed on one surface of the base material;
a solder powder-containing adhesive layer formed on one surface of the adhesive layer; and
a solder powder layer formed on one surface of the solder powder-containing adhesive layer, wherein the solder powder layer contains solder powder arranged in a sheet form,
wherein the solder powder-containing adhesive layer contains a mixture of solder powder and an adhesive component so as to have a thickness that a predetermined amount of solder is contained.
2. The solder transfer sheet according to claim 1 , wherein the solder powder layer contains solder powder arranged in a one-layer sheet form.
3. The solder transfer sheet according to claim 1 , wherein the adhesive component of the solder powder-containing adhesive layer comprises a compound that is not volatilized at a melting point of the solder powder.
4. The solder transfer sheet according to claim 1 , wherein the adhesive component of the solder powder-containing adhesive layer contains a side-chain crystalline polymer, the adhesive component having flowability at a temperature equal to or higher than a melting point of the side-chain crystalline polymer to exhibit adhesive force and the adhesive component being crystallized at a temperature lower than the melting point of the side-chain crystalline polymer to reduce the adhesive force thereof.
5. The solder transfer sheet according to claim 4 , wherein the side-chain crystalline polymer has a melting point of 30° C. or higher but lower than 70° C.
6. The solder transfer sheet according to claim 4 , wherein the adhesive component has an adhesive force of less than 2.0 N/25 mm at a temperature of lower than the melting point of the side-chain crystalline polymer.
7. The solder transfer sheet according to claim 1 , wherein a volume ratio between the solder powder and the adhesive component constituting the solder powder-containing adhesive layer is 74 to 26.
8. A method for solder precoating using a solder transfer sheet comprising:
applying an adhesive onto a base material to form an adhesive layer;
forming a solder powder-containing adhesive layer containing solder powder and an adhesive on the adhesive layer;
sprinkling solder powder onto the solder powder-containing adhesive layer;
removing an excess of the solder powder on the solder powder-containing adhesive layer to form a solder powder layer;
laying the solder powder layer of a solder transfer sheet having the adhesive layer, the solder powder-containing adhesive layer, and the solder powder layer on top of an electrode side of a workpiece;
applying heat and pressure at the same time on an object obtained by laying the solder transfer sheet on top of the workpiece; and
removing the solder transfer sheet after solder solidification.