No-clean low-residue solder paste for semiconductor device applications
View Patent ↗A no-clean low residue solder paste is described for die-attach dispensing or fine pitch printing of semiconductor devices. The solder paste has a homogeneous consistency with no tendency to paste separation. The ultimately remaining residue is clear and crystal like and is compatible with further processing steps without prior cleaning with a solvent to remove flux residue. The solder paste comprises a relatively low amount of rosin in combination with a viscous solvent system, thixotropic agents, activators, additives and optionally plasticizers.
1. Solder paste for die-attachment of semiconductor devices comprising a solder powder dispersed in a flux, the flux comprising a homogeneous mixture of a solvent system, at least one thixotropic agent, at least one activator, and a rosin, wherein the solvent system comprises one or more glycol ethers, and one or more alcohols, and a highly viscous solvent and/or solid solvent at room temperature and the concentration of the solvent system amounts to 55 to 75 wt.-% and the concentration of the rosin amounts to 10 to 25 wt.-%, each relative to the total weight of the flux and wherein the highly viscous solvent and/or solid solvent are selected from the group consisting of trimethylopropane, 1,2-octanediol, 1,8-octanediol, isobornyl cyclohexanol or a combination thereof.
2. Solder paste for die-attachment of semiconductor devices according to claim 1 , wherein the highly viscous solvent and/or solid solvent of the solvent system are vaporized during reflow soldering process.
3. Solder paste according to claim 1 , wherein the glycol ether is selected from the group consisting of mono-, di- or tri-propylene glycol methyl ether, mono-, di-, or tri-propylene glycol n-butyl ether, mono-, di-, or tri-ethylene glycol n-butyl ether, ethylene glycol methyl ether, tri-ethylene glycol methyl ether, di-ethylene glycol di-butyl ether, tetra-ethylene glycol di-methyl ether, or a combination thereof.
4. Solder paste according to claim 3 , wherein the alcohols are selected from the group consisting of 2-ethyl-1,3-hexanediol, n-decyl alcohol, 2-methyl-2,4-pentanediol, terpineol and isopropanol or mixtures thereof.
5. Solder paste according to claim 4 , wherein the rosin is selected from the group consisting of tall oil rosin, hydrogenated rosin, partially hydrogenated rosin, dehydrogenated rosin or a combination thereof.
6. Solder paste according to claim 5 , wherein the thixotropic agent is selected from the group consisting of glyceryl tris-12-hydroxy stearate, modified glyceryl tris-12-hydroxy stearate, polyamide, stearamide or a combination thereof.
7. Solder paste according to claim 6 , wherein the activator comprises organic acids selected from the group consisting of caproic acid, phenyl-acetic acid, benzoic acid, salicylic acid, aminobenzoic acid, 4-n-butylbenzoic acid, 4-t-butylbenzoic acid, 3,4-dimethoxybenzoic acid, oxalic acid, succinic acid, maleic acid, malic acid, adipic acid, malonic acid and mixtures thereof and the activator further comprises an amine selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, isopropanolamine or a combination thereof.
8. Solder paste according to claim 7 , wherein the paste further comprises an additive selected from the group consisting of ethoxylated amine rosin, amine rosin, methyl ester of rosin, n-oleylsarcosine and oleyl imidazoline or mixtures thereof.
9. Solder paste according to claim 8 , wherein the flux comprises 1 to 6 wt.-% of thixotropic agent, 10 to 20 wt.-% of activators and 0.5 to 3 wt.-% of additives each relative to the total amount of flux.
10. Solder paste according to claim 9 , wherein the solvent system comprises 30 to 50 wt.-% of a very viscous solvent and/or solid solvent at room temperature, 10 to 30 wt.-% of glycol ether and 10 to 20 wt.-% of alcohols, and the activators comprise 5 to 15 wt.-% of an acid and 1 to 10 wt.-% of an amine, each relative to the total amount of flux.
11. Solder paste according to claim 10 , wherein the solder powder is selected from lead containing solder alloys or lead free solder alloys.
12. Solder paste according to claim 11 , wherein the lead containing solder alloy is selected from PbSn-, PbSnAg-, PbAg- or PbInAg-alloys with at least 85 wt.-% of lead.
13. Solder paste according to claim 8 , wherein the paste further comprises a plasticizer selected from the group consisting of dimethyl phthalate, dibutyl phthalate, diisodecyl phthalate, butyl oleate, diisobutyl adipate, dioctyl adipate, dipropylene glycol dibenzoate, dioctyl sebacate and mixtures thereof.
14. Solder paste according to claim 13 , wherein the flux comprises 1 to 6 wt.-% of thixotropic agent, 10 to 20 wt.-% of activators and 0.5 to 3 wt.-% of additives, and 0.1 to 2 wt.-% of plasticizers, each relative to the total amount of flux.
15. Solder paste according to claim 14 , wherein the solvent system comprises 20 to 40 wt.-% of a very viscous liquid and/or solid solvent at room temperature, 30 to 50 wt.-% of alcohols, and the activators comprise 5 to 15 wt.-% of an acid and 1 to 10 wt.-% of an amine, each relative to the total amount of flux.
16. Solder paste according to claim 15 , wherein the solder powder is prepared from a lead containing or a lead free solder alloy.
17. Solder paste according to claim 16 , wherein the lead containing solder alloy is selected from SnPb-, SnPbAg-, SnPbBi-, and PbSnSb-alloys.
18. Solder paste according to claim 16 , wherein the lead free solder alloy is selected from SnAgCu-, SnAg-, SnCu-, SnCuIn-, SnAgCuSb-, SnAgSb-, SnSb- or BiSn-alloys.