非离子表面活性剂对助焊剂润湿性能的影响

在软钎焊免清洗助焊剂中分别添加了3种不同含量的非离子表面活性剂:TritonX—100、Tween—20和PEG2000,得到了3组助焊剂。使用这3组助焊剂和Sn0.7Cu无铅钎料在纯铜板上进行了铺展测试。结果表明,添加TritonX—100和添加Tween—20的质量分数均为0.6%时,钎料的润湿角最小值分别为30.07°和29.70°,铺展面积最大值分别为56.67mm2和58.53mm2;添加PEG2000质量分数为0.3%时,钎料的润湿角最小值为26.70°,铺展面积最大值为66.88mm2,比未添加时增加26.9%。适量加入非离子表面活性剂能够改善助焊剂的润湿性,并提高无铅钎料的铺展能力。     

Contact angle measurements of Sn-Ag and Sn-Cu lead-free solders on copper substrates

In this study, the contact angles of four lead-free solders, namely, Sn-3.5Ag, Sn-3.5Ag-4.8Bi, Sn-3.8Ag-0.7Cu, and Sn-0.7Cu (wt.%), were measured on copper substrates at different temperatures. Measurements were performed using the sessile-drop method. Contact angles ranging from 30° to 40° after wetting under vacuum with no fluxes and between 10° and 30° with rosin mildly activated (RMA) and rosin activated (RA) fluxes were obtained. The Sn-3.5Ag-4.8Bi exhibited the lowest contact angles, indicating improved wettability with the addition of bismuth. For all soldering alloys, lower contact angles were observed using RMA flux. Intermetallics formed at the solder/Cu interface were identified as Cu₆Sn₅ adjacent to the solder and Cu₃Sn adjacent to the copper substrate. The Cu₃Sn intermetallic phase was generally not observed when RMA flux was used. The effect of temperature on contact angle was dependent on the type of flux used.     

无铅药芯焊锡丝用非松香基固体助焊剂的研究

针对现有松香固体助焊剂活性温度低和焊后变色的问题,研制了以十八酸、聚乙二醇和少量耐热松香作为载体,以己二酸和癸二酸复配作为活性剂的非松香基固体助焊剂.此助焊剂常温下为白色膏状,熔点范围110℃～130 ℃,满足Sn-0.7Cu无铅药芯焊锡丝灌芯和拔丝工艺.助焊剂中各成分沸点在300℃左右,满足手工烙铁焊高温要求且大大减...     

Wetting and reaction of Sn-2.8Ag-0.5Cu-1.0Bi solder with Cu and Ni substrates

The wettability of newly developed Sn-2.8Ag-0.5Cu-1.0Bi lead-free solder on Cu and Ni substrates was assessed through the wetting balance tests. The wettability assessment parameters such as contact angle (ϑ_c) and maximum wetting force (F_w) were documented for three solder bath temperatures with three commercial fluxes, namely, no-clean (NC), nonactivated (R), and water-soluble organic acid flux (WS). It was found that the lead-free Sn-2.8Ag-0.5Cu-1.0Bi solder exhibited less wetting force, i.e., poorer wettability, than the conventional Sn-37Pb solder for all flux types and solder bath temperatures. The wettability of Sn-2.8Ag-0.5Cu-1.0Bi lead-free solder on Cu substrate was much higher than that on Ni substrate. Nonwetting for Sn-2.8Ag-0.5Cu-1.0Bi and Sn-Pb solders on Ni substrate occurred when R-type flux was used. A model was built and simulations were performed for the wetting balance test. The simulation results were found very close to the experimental results. It was also observed that larger values of immersion depth resulted in a decrease of the wetting force and corresponding meniscus height, whereas the increase in substrate perimeter enhanced the wettability. The wetting reactions between the solder and Cu/Ni substrates were also investigated, and it was found that Cu atoms diffused into the solder through the intermetallic compounds (IMCs) much faster than did the Ni atoms. Rapid formation of IMCs inhibited the wettability of Sn-2.8Ag-0.5Cu-1.0Bi solder compared to the Sn-Pb solder.     

Solderability testing of 95.5Sn-3.9Ag-0.6Cu solder on oxygen-free high-conductivity copper and Au-Ni-Plated kovar

The solderability of 95.5Sn-3.9Ag-0.6Cu solder on oxygen-free high-conductivity (OFHC) copper and Au-Ni-plated Kovar was examined as a function of flux and process temperature. The three solder fluxes included a rosin-based (R) material, a rosin mildly activated (RMA) flux, and a low-solids (LS) flux. The solderability metric was the contact angle, θ_C, measured by a meniscometer and wetting-balance techniques. The wetting rate and time to maximum force parameters were also documented. In most cases, the contact angles for the 95.5Sn-3.9Ag-0.6Cu solder alloy, regardless of the type of flux or temperature, were higher then those for the 63Sn-37Pb eutectic-solder alloy, indicating a less “solderable” surface.     

无铅焊膏工艺适应性的研究

无铅焊膏是适应环保要求的一种绿色焊接材料,其质量的优劣直接决定着现代表面组装组件品质的好坏,为了检测与评价无铅焊膏的性能,研究影响其焊接可靠性的因素,实验研制了一种Sn-Ag-Cu无铅焊膏,并根据其本身的材料特性和实际工艺性能结合IPC的有关标准设计了整套试验,包括:焊膏黏度测试、塌陷实验、焊球实验以及铜板腐蚀测试等。研究结果表明:焊粉的质量分数与焊膏黏度呈正比关系;高温高湿环境下焊膏的可靠性降低,焊后残留物的腐蚀性增强;焊膏过多暴露在氧化环境中易引起焊料成球等焊接缺陷。     

Development of lead-free wave soldering process

Lead-free wave soldering was studied in this work using a 95.5Sn/3.8Ag/0.7Cu alloy. A process DOE was developed, with three variables (solder bath temperature, conveyor speed, and soldering atmosphere), using a dual wave system. Four no-clean flux systems, including alcohol- and water-based types, were included in the evaluation. A specially designed "Lead-Free Solder Test Vehicle", which has various types of components, was used in the experiments. Both organic solderability preservative (OSP) and electroless nickel/immersion gold (Ni/Au, or ENIG) surface finishes were studied. Soldering performance (bridging, wetting and hole filling) was used as the responses for the DOE. In addition, dross formation was measured at different solder bath temperatures and atmospheres. Dross formation with Sn/Ag/Cu bath was compared to that with eutectic Sn/Pb bath. Regarding the connector-type component, a pad design giving the best soldering performance was evaluated based on the DOE results. Finally, a confirmation run with the optimum flux and process parameters was carried out using the Sn/Ag/Cu solder, and a comparative run was made with the Sn/Pb solder alloy and a no-clean flux used in production. The soldering results between the two runs indicate that with optimum flux and process parameters, it is possible to achieve acceptable process performance with the Sn/Ag/Cu alloy.     

Wetting interaction of Pb-free Sn-Zn-Al solders on metal plated substrate

A newly developed Pb-free Sn-9(Zn-5Al) solder was investigated for its wetting behavior on metal plated Cu substrate. The Cu substrate was plated with electroless nickel (EN) or with EN/Cu multilayer plating. The wetting behavior was investigated with a wetting balance which gave rise to a wetting curve. Fluxes including L-glutamic acid and dimethylammonium chloride were applied for enhancing the wetting behavior. The solder was unable to wet the EN plated Cu substrate without the assistance of flux until temperatures of 460°C and above. The material interaction between the solder and the substrate at this high temperature was investigated with scanning electron microscope elemental analysis. The wetting temperature between solder and EN plated copper was lowered to 310°C with the application of the above fluxes. The further incorporation of a layer of Cu plating with the EN layer further lowered the wetting temperature to 250°C.     

无焊剂软钎焊技术研究

无焊剂软钎焊技术因其焊接过程中无焊剂残留,被广泛应用于光电器件和芯片倒装焊等方面。首先对无焊剂软钎焊的原理和工艺进行了阐述,并指出气氛保护和等离子处理是无焊剂软钎焊的两个主要技术途径。基于上述分析,采用无焊剂软钎焊工艺开展钎料润湿性研究。结果表明,还原气氛保护和等离子处理后,焊料的润湿铺展性能显著提高。     

Influence of flux on wetting behavior of lead-free solder balls during the infrared-reflow process

The effects of two different fluxes (A6 and B6) on the wetting performance of Sn-3.5Ag-0.5Cu lead-free solder balls were investigated during the reflow process. Solder ball wetting behavior in real time via an optical microscope coupled with a video recorder during the reflow process was studied. The lead-free solder balls started to melt and wet at 210°C by using A6, which is 8°C lower than the melting point (218°C) of the solder material used. The wetting performance of the lead-free solder ball was dramatically enhanced by using A6. The wettability test indicated that the height of the solder ball after the reflow process with flux A6 was significantly lower than that with B6. It was found that strong fluxing capability caused these phenomena.     

Wetting and Soldering Behavior of Eutectic Au-Ge Alloy on Cu and Ni Substrates

Au-Ge-based alloys are interesting as novel high-temperature lead-free solders because of their low melting point, good thermal and electrical conductivity, and high corrosion resistance. In the present work, the wetting and soldering behavior of the eutectic Au-28Ge (at.%) alloy on Cu and Ni substrates have been investigated. Good wetting on both substrates with final contact angles of 13° to 14° was observed. In addition, solder joints with bond shear strength of 30 MPa to 35 MPa could be produced under controlled conditions. Cu substrates exhibit pronounced dissolution into the Au-Ge filler metal. On Ni substrates, the NiGe intermetallic compound was formed at the filler/substrate interface, which prevents dissolution of Ni into the solder. Using thin filler metal foils (25 μm), complete consumption of Ge in the reaction at the Ni interface was observed, leading to the formation of an almost pure Au layer in the soldering zone.     

Flux development for lead-free solders containing zinc

New lead-free solders containing zinc are promising candidates to replace near-eutectic tin-lead solders because the solders melt at lower temperatures than Sn-Ag-base solders. They also possess good mechanical and fatigue properties and are less expensive. However, the contact angle on copper for Sn-Zn solders is high when fluxes used for Sn-Pb solders are utilized. A novel approach for flux development to improve wetting of copper surfaces by tin-zinc eutectic solder was developed: tin containing organic compounds, which decomposes at soldering temperatures and produces metallic tin on surfaces to be soldered was added to several specially formulated fluxes. This process improves wetting of copper surfaces by molten tin-zinc eutectic solder. Fluxes were developed that give a contact angle as low as 20°.     

Solderability testing of Sn-Ag-XCu Pb-free solders on copper and Au-Ni-plated kovar substrates

Solderability was evaluated for four Pb-free alloys: 95.5Sn-4.3Ag-0.2Cu (wt.%), 95.5Sn-4.0Ag-0.5Cu, 95.5Sn-3.9Ag-0.6Cu, and 95.5Sn-3.8Ag-0.7Cu on oxygen-free electronic grade (OFE) Cu and Au-Ni plated Kovar substrates. The solderability metric was the contact angle, θ_c, as determined by the meniscometer/wetting balance technique. Tests were performed at 230°C, 245°C, and 260°C using rosin-based, mildly activated (RMA) flux, a rosin-based (R) flux, and a low-solids (LS) flux. The Pb-free solders exhibited acceptable to poor solderability (35°<θ_c<60°) on Cu with the RMA flux. Nonwetting occurred in most tests using the R flux. Wetting was observed with the LS flux, but only at 245°C and 260°C and with high contact angles. The solderability of the Pb-free solders improved at all test temperatures on the Au-Ni plated Kovar substrate when using the RMA flux (30°<θ_c<50°). Wetting was observed with the R flux (35°<θ_c<60°) and LS flux (50°<θ_c<85°) for all temperatures. The Pb-free solders had generally lower wetting rates and longer wetting times on Cu than the 63Sn-37Pb solder. The wetting rate and wetting time data were superior on the Au-Ni plated Kovar substrates. In general, solderability, as measured by θ_c along with the wetting rate and wetting time, did not exhibit a consistent dependence on the composition of the Sn-Ag-XCu (X=0.2, 0.5, 0.6, and 0.7) alloys. The better performers were 95.5Sn-3.9Ag-0.6Cu alloy with the RMA flux (both Cu and Au-Ni plated Kovar) and 95.5Sn-3.8Ag-0.7Cu with the R and LS fluxes (Au-Ni-Kovar, only). The solder-flux interfacial tension, γ_LF, had a significant impact on the θ_c values. The magnitudes of the contact angle θ_c suggested that the four Pb-free solders would experience higher solderability defect counts at the printed wiring assembly level.     

Sn–Ag–Cu Soldering Reliability as Influenced by Process Atmosphere

To develop an optimal surface mount reflow soldering process with Sn–Ag–Cu, the influences of atmosphere and cooling speed on soldering reliability have been examined by using Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB). Typical three Sn–Ag–Cu alloy pastes, i.e., Sn–3.0wt%Ag–0.5wt%Cu, Sn–3.8wt%Ag–0.75wt%Cu, and Sn–4.0wt%Ag–0.9wt%Cu, were used for reflow soldering in air or ${hbox {N}} _{2}$ atmospheres. In the case of chip component joints, the solder compositions, cooling speed, and atmospheres during reflow treatment slightly affect the dendritic microstructure of the solder fillets. In contrast, these parameters rarely affect the solder wettability both on boards/components and shear strengths of the solder joints. In the case of the SOP joints, however, the atmospheres in reflow treatment and the fluxes strongly affect the appearances of solder fillet surfaces structure. Despite the types of solder fluxes, ${hbox {N}} _{2}$ process atmosphere obviously improved wettability of the solders on the lead-frames of the SOP. Moreover, the scatter in shear strengths becomes smaller and the wetting of solders on the lead-frames becomes stabler in ${hbox {N}} _{2}$ atmosphere than in air atmosphere.      

Sn-9Zn合金无铅钎料用助焊剂研究

通过测量润湿面积和润湿角,研究不同助焊剂对Sn-9Zn焊料润湿性的影响。结果表明:助焊剂对Sn-9Zn焊料润湿性影响很大,由乳酸、聚乙二醇和SnCl2所构成的助焊剂与Sn-9Zn焊料有很好适应性;同时扫描电镜和能谱分析也表明焊料与Cu基体界面的IMC为Cu5Zn8相,比Sn-37Pb焊料具有更高的剪切强度。     

SnAgCuRE系钎料合金的润湿特性

选择商用水溶性钎剂,以润湿平衡法,研究了SnAgCuRE系钎料合金在表面贴装元器件上的润湿特性。结果表明:当w(RE)为0.1%时,预热15s,255℃钎焊5s,该钎料合金具有最大的润湿力1.510mN和最小的润湿角11.03°,与传统的Sn63Pb37钎料的润湿力相当,可满足表面组装元器件对其润湿性能的要求。     

Effect of flux on the wetting characteristics of SnAg, SnCu, SnAgBi, and SnAgCu lead-free solders on copper substrates

The effect of flux on the wetting characteristics of four lead-free solders, Sn-3.5Ag, Sn-0.7Cu, Sn-3.5Ag-4.8Bi, and Sn-3.8Ag-0.7Cu (wt.%), on copper substrates have been studied at 240, 260, and 280°C. The fluxes investigated were rosin (R), mildly activated rosin (RMA), and activated rosin (RA). The wetting tests were conducted using the sessile-drop method. Results showed that fluxes significantly affect the wetting properties of the solders. Contact angles ranging from 10° to 30° for RMA, 20° to 30° for RA, and 35° to 60° for R were obtained. The effect of temperature on contact angle depended on the type of flux used. The contact angle decreased with increasing temperature; however, in some cases the contact angle was independent of temperature. The Sn-3.5Ag-4.8Bi exhibited the lowest contact angles indicating improved wettability with addition of bismuth. The microstructure of the solder/copper interface was analyzed by scanning electron microscopy.     

Interdiffusion analysis of the soldering reactions in Sn-3.5Ag/Cu couples

Extensive microstructural and kinetic studies on the formation and growth of the intermetallics of Sn-rich solder/Cu couples have been reported. However, experimental data on the interdiffusion mechanisms during soldering reactions are limited and in conflict. The interdiffusion processes for soldering of Sn-3.5Ag alloy/Cu couples were investigated by using the Cr-evaporated surface as a reference line. At the beginning of soldering, Cu was observed to outdiffuse to the molten Sn−3.5Ag alloy until saturation, and the Sn−Ag solder dissolved with Cu collapsed below the reference line. As a result, the scallop-shaped Cu₆Sn₅ intermetallic compound was formed at the newly-formed Sn−Ag−Cu solder/Cu interface below the original Cu surface. When the soldered joint was reflowed at the lower temperature to suppress the Cu dissolution, the Cu₆Sn₅/Cu interface moved into the Cu substrate. Therefore, Sn is the dominant diffusing species for the intermetallic formation during the soldering process, although the extensive Cu dissolution occurs at the early stage of soldering.     

Solderability of pre-tinned Cu sheet

The reliability and integrity of pre-tinned copper-clad printed circuit (PC) boards are serious concerns in the manufacture of electronic devices. The factors that influence the wetting during soldering of Cu are discussed. The results suggest that pre-tinning with a Pb-rich solder, such as 95Pb-5Sn, is preferred to pre-tinning with eutectic solder, since the latter can develop exposed intermetallics during aging that wet poorly. The results also confirm that the use of flux leads to carbon contamination in the solder.     

Study on Cu particles-enhanced SnPb composite solder

The Sn-Pb solder is widely used in the electronics industry. With the development of surface mount technology and miniaturization of elements, mechanical properties of the solder are critical. Creep resistance and size stability of soldered joints are important for optical electronics. In the present work, Cu particles with a size of about 8 μm were added to the eutectic 63Sn-37Pb solder to improve the creep property of the soldering alloy. The contents of the Cu particles are 5 vol.% and 10 vol.% separately. The solder matrix is 63Sn37Pb particles with a normal size of 43 μm. The composite solder pastes are manufactured from a mixture of these particles with no-clean flux. Under reflow soldering, the metal particles were uniformly dispersed in the Sn-Pb alloy, and very thin intermetallic compounds were formed between the particles and matrix. To simulate practical soldering of printed circuit boards, a specially designed mini specimen with lap joint is used for the creep-rupture test. For the condition of ambient temperature, the creep-rupture lifetime of the soldered joint can be increased by one order quantitatively using the composite solder compared to the 63Sn37Pb eutectic solder. Other mechanical properties are measured also. In addition, the wetting property of the enhanced solder is good through the wettability test.