Improvement Of Stability Of Copper Wire Bonding

Copper is widely applied in various fields with excellent conductive thermal conductivity, polishing, ductility.The resistance of the bare copper wire (135 ?/m) is lower 22% than the gold wire (180 ?/m), and thermal conductivity of bare copper wire (392 w/m.k) is nearly 25% than the gold wire (310w/m.k). Because the gold price is higher, many packaging companies are increasing spending on copper wire process, but the copper wire long exposed easily oxidized in the air, easy to reduce the quality of the semiconductor packaging.In order to improve the quality of copper wire bonding, which prevent the oxidation of the copper wire, this article through the following two kinds of surface treatment technology to improve the stability of the copper wire bonding.(1) Plating a layer of oxidation resistance good palladium coating on the surface of the copper by the method of electroless plating to improve the bonding quality of copper wire, the key research solution formulation and operating conditions on the quality of the electroless palladium.By means of stabilizing agent, complexing agent, plating temperature and time of study, found that different concentrations of stabilizing agent, complexing agent and plating temperature and time have obviously influenced on the stability of the plating solution, plating speed, the appearance of the coating and porosity. Through parameter optimization, we get suitable formula for copper electroless plating of palladium:PdCl2 2 g/L, NaH2PO2·H2O 12 g/L,38%(mass fraction) HC14 mL/L,28%(mass fraction) of NH3·H2O 160 mL/L, bismuth nitrate 55 mg/L, isopropanolamine 25 mL/L and pH 9.8±0.2 mm.The best plating conditions is 52 ?,35 min.At the maximum deposition rate is 1.16 mg/cm2·h, and the coating has the smallest corrosion current density(3.24×10-9 A/cm2), the highest corrosion resistance (4.41×106 ?/cm2) and the lowest corrosion rate (4.60×10-5mm/a), no change to pH, good solution stability;SEM photo shows that the coating is compact and uniform, no visible flaws and pinhole, palladium particle size is 100-200 nm;The EDS results showed that phosphorus content is 5% in surface coating.XRD showed the palladium plating exist in micro crystalline state;Due to difference of the surface of copper wire and copper, copper wire surface caused activation energy of palladium deposition is smaller, by increasing the concentration of isopropyl alcohol amine to control the growth of palladium particles, suitable for copper electroless plating of palladium formula and process:PdCl2 2 g/L,12 g/L NaH2PO2·H2O,38%(mass fraction) HCl4 mL/L,28%(mass fraction) of NH3·H2O 160 mL/L, and nitration of bismuth 55 mg/L, auxiliary complexing agent isopropanolamine 35 mL/L, pH 9.8, temperature and time is 52 ??35 min,respectively.Can be seen from the SEM diagram, on the surface of coating is careful, no to take off the floor, crack phenomenon.(2) The use of corrosion inhibitors on copper surface processing to improve the oxidation resistance of copper.With BTA as the main corrosion inhibitor, and study its optimum concentration, processing temperature and time, and with BTA/ethanol/sodium molybdate as the foundation, through its with inorganic, organic and polymer blends to form film on the copper surface, and discusses their synergies, determine the best proportion between them.The main results were as follows:with water as medium, single BTA as corrosion inhibitor, by means of BTA concentration, processing temperature and time of study and comparison, get the best BTA concentration, processing temperature and processing time is 3 g/L,40?,10 min, respectively under the condition of the corrosion rate is 5.31×10-4 mm/a, bubble time of copper surface is 15 s.The addition of ethanol can improve the corrosion resistance of BTA on copper surface, when the concentration of ethanol for 50 ml/L, the corrosion rate is 2.33×10-4 mm/a, compared to the single system with BTA 5.31 x 10-4 mm/a,corrosion rate decreased by 56%. Bubble time of copper surface is 23s.On this basis, study the different concentrations of sodium molybdate/BTA/ethanol system influence on its effects of copper, the best concentration of sodium molybdate for 4 g/L, the corrosion rate under the condition is 2.12×10-4 mm/a, compared to BTA/ethanol system,2.33×10-4 mm/a,the corrosion rate further reduce. Bubble time of copper surface is 27 s.In addition, study the influence of adding cerium nitrate, sodium molybdate system OP and polyethylene glycol in the BTA/ethanol/on the system.The results showed that the addition of other species has a certain impact on its effect.The present data show that the OP effect is better than the cerium nitrate and polyethylene glycol.