芯片焊锡工程能力分析.docVIP

芯片焊锡工程能力分析 沈泽斌三星电子(苏州)半导体有限公司 摘 要:SMT技术已经在电子组装技术中广泛运用,随着SMT的进一步发展，使电子产品向更高小型化和更高超的性能发展,也导致需要增加环路密度和有关可靠性的提高. 然而,芯片产品的焊锡的工程能力-对于SMT生产更小电子产品流程有着致关的重要性. 通过本人在生产实践中一系列的研究以后,对于镀层(镍&锡)厚度和强度对芯片的电特性有着密切的关系.在本论文中中,对焊锡的工程能力和焊接情况的用实验加以证明.此外,焊锡在不同情况下，对工程中焊锡发生偏移也是评价内容之一.实验评价的结果显示覆镀厚度对焊锡-工程能力是最为重要的参数. Chip solder-ability analysis zebin.shenSamsung Electronics （SUZHOU）Semiconductor Abstract:SMT is used as an updated electronic assembly technology,it makes electronic products move towards higher miniaturization and higher performance, leads to increased circuit density and high demands on reliability. Device solder-ability is critical to the process of SMT, which impacts the electric properties of electronic products. After a series of studies, the parameters of chip plating (Nickel &Tin film) thickness and current intensity may have relation to soldering system. In this paper, the viewpoint has been demonstrated by evaluation of solder ability and soldering performance. In addition, test of pullback ability when misalignment is also one of the evaluating points. Result of the evaluation show that chip plating thickness is a most important parameter to Solder-ability system. 正 文1. Prologue Soldering system is a substantial part during the chymist compatibility process. The definition of the soldering system is refer to all the chemic materials such as solder paste, soldering flux, device and so on. The metal which could soldering, such as copper、nickel、 gold、 silver etc, these metal will quickly form a film with solder similarly to a kind of compound called Intermetallic compound (IMC) when at high temperature. At the moment of the fused tin contact with copper, solder wetting would happen. Tin atoms immediately diffuse to the copper film and at the same time copper atoms diffuse to the tin film, on their common boundary IMC of Cu6Sn5 was formed. Depending on IMC all devices are jointed with pad on PCB. Chip solder-ability is a portion of soldering system and is also the emphasis in this paper. Considering the thickness of plating films and plating current condition, large quantities of experiments and tests are organized to evaluate chip solder-ability. Solder performance、solder joint strength and the reversion ability after misalignment are the items refer to.2. Evaluation of solder performance2.1Sn/Ni thickness analysis In this study, the structure of chip plating-SnNi with 1 Sn、2Sn、1 Niand2 Ni is evaluated, see figure1.(a) 1Sn (b) 2Sn(c) 1Ni(d) 2NiFigure.1 Plating-SnNi structure studied The wetting balance test is a powerful toll for quantitative measuring the solder-ability, the checker demonstrates its full capability for improving and controlling the soldering process of materials placed under micro-soldering with highprecision. The chip immersed in a bath of molten solder (Sn96.5 Ag3.0 Cu0.5) at 245for 15sec. Wetting is a dynamic event and in the actual soldering process, the time above the melting point of solder is limited. Therefore, the wetting force together with the wetting time (e.g. the time to reach 2/3 of the maximum wetting force) is good characteristics to judge the solder-ability in a wetting balance test. Table.1Wetting balance test resultTest items1 Sn2 Sn1 Ni2 NiZero-crossing time1.921.802.591.75Wetting time1.080.170.420.14Total wetting time3.001.973.011.88Maximum force0.170.190.110.25End force0.100.130.050.18Remark: Total wetting time 3s.Figure.2 Wetting balance curve for 1 Sn & 1 NiFigure.3 Wetting balance curve for 2 Sn & 2 Ni Table.1 shows wetting balance test result for 1 Sn、2Sn、1 Niand2 Ni, we can clearly see that the thickness of Nickel &Tin film have directly effect wetting ability. The less of thickness, the poorer of solder-ability. Another test for solder-ability is qualitative experiment.Condition:Steam 4hours(Humidity100,Temp98)；Dip in 2455；Solder bath for 20.5sCriterion: Good tinning (95% covered) Table.2Solder-ability test result:Test items1 Sn2 Sn1 Ni2 NiFail/Total quantity4/52/53/52/5 The conclusion has been proved again by solder-ability test, so in order to improve chip solder-ability the parameter of plating-SnNi thickness must be under good controlled.2.2Current intensity analysisThe value of plating current and plating time haverelated to crystal diameter and distribution which may also effect wetting quality. Figure.4 50A 12minutes Figure.5 30A 20minutes Figure.6 10A 60minutesThe above three pictures respectively show plating crystal structure (SEM photos magnify 350) on different current conditions. It is obvious that to meet with a certain plating thickness, the smaller current value and longer plating time, the more dense distributing we would gained.Considering the three referred instances test of wetting balance and solder-ability are done. Table.3 Wetting balance test resultTest items50A 12min30A 20min10A 60minZero-crossing time1.921.841.74Wetting time0.590.060.27Total wetting time2.511.902.00Maximum force0.200.270.26End force0.100.180.17Figure.7 Wetting balance curve for current parameterThe result of wetting balance indicate all of the three conditions meet with wetting require (Total wetting time 3s).In addition, the result of solder-ability test for this three current conditions shown as the following table. Data from the experiments above show that plating thickness has more infection to solder-ability system compared with plating current intensity. Table.4Solder-ability test result:Test items50A 12min30A 20min10A 60minFail/Total quantity0/50/50/53. Evaluation of solder joint strength3.1Bending test Bending test is done to determine the force limit which chip can afford. Chips are mounted in center of 90mm board length, bending 5mm for 5sec with the speed of 60mm/min. Chips on all kinds of conditions studied in this paper have passed this test.Table.5Bending test result:ItemPre-test(K)POST-test(K)R%1 Sn0.99470.99520.04832 Sn0.99850.99950.10021 Ni0.99940.9991-0.03102 Ni0.99390.99450.059450A 12min0.99590.99660.064330A 20min0.99780.99880.096210A 60min0.99790.99890.1062Remark: (2.0%+0.05) no mechanical damage3.2Adhesive strength of termination test Termination adhesive test is done to determine the force needed to push from side of the chip which mounted on board. Applying 5N pressure for 10sec, and we find no mechanical damage or sign of disconnect for the above seven conditions.4. Evaluation of pull back abilitySimulation experiment has also been done to validate influencing factors. In order to check the solder-ability, mount machine was adjusted for 50% misalignment and observe their pull back ability after reflow. Figure.8 50% misalignment mountTable.6Pull back test result:ItemMisalign/Total1 Sn6/502 Sn0/501 Ni3/502 Ni0/5050A 12min1/5030A 20min0/5010A 60min0/50Table.6 shows pull back ability when misalignment according to different conditions. It is clear to see that both plating thickness and plating current parameters could affect chip solder-ability. Normally, 50% mount misalignment could be pulled back after reflow, but less plating thickness and rougher crystal arrangement would embody their poor solder-ability.(a) good pull back ability(b) poor pull back abilityFigure.9 after reflow statusFigure.9 stands for chip pull back ability after reflow, at the same mount condition(X-direction 50% misalignment) but display different pull back ability according to different chip plating parameters. 5. Conclusion Chip plating state is critical to its solder-ability, the evaluation of solder performance、solder joint strength and pull back ability is done to validate the effect factors, the final purpose is through the management of device plating condition to improve SMT process and gain better quality of products. Summarize to a series of tests referred, general conclusion is:Chip nickel film and tin film plating thickness, especially tin film thickness is the most important parameter to soldering system, less thickness would lead to poorer solder-ability, generally