Gold Plating Thickness Research Articles

Dissolution Rate of Electronics Packaging Surface Finish Elements in Sn3.0Ag0.5Cu Solder

A clear understanding of the characteristics of solder wetting to component terminations is critical for establishing thermal process profiles that ensure acceptable solder joint integrity. For example, component gold plating thickness as well as the soldering process temperature and time must be carefully controlled to prevent embrittlement by the gold/tin intermetallic compound. The electronics industry has successfully applied the results published in 1969 by W.G. Bader to relate process temperature and time to surface finish dissolution rates in defining acceptable soldering process profiles for tin/lead surface finishes. To date, there is no single comprehensive data set for these materials that is comparable to the Bader work. To address this need, solder dissolution experiments modeled on the Bader work were conducted using Sn3.0Ag0.5Cu (SAC305) solder with gold, silver, palladium, platinum, copper and nickel samples. In these experiments, samples were immersed in a solder pot, and the resulting material dissolution was determined for different solder temperatures and immersion times. This paper describes the test approach for measuring the solder dissolution of these materials and tabulates dissolution rates suitable for optimizing soldering process profiles for electronic assemblies. The dissolution rates of the surface finish materials were found to typically be about 50% higher for the lead-free SAC305 solder than tin–lead solder.

Thermal gap conductance at low contact pressures (

Thermal contact conductance (TCC) measurements are made on bare and gold plated (⩽0.5 μm) oxygen free high conductivity (OFHC) Cu and brass contacts in vacuum, nitrogen, and argon environments. It is observed that the TCC in gaseous environment is significantly higher than that in vacuum due to the enhanced thermal gap conductance. It is found that for a given contact load and gas pressure, the thermal gap conductance for bare OFHC Cu contacts is higher than that for gold plated contacts. It is due to the difference in the molecular weights of copper and gold, which influences the exchange of kinetic energy between the gas molecules and contact surfaces. Furthermore, the gap conductance is found to increase with increasing thickness of gold plating. Topography measurements and scanning electron microscopy (SEM) analysis of contact surfaces revealed that surfaces become smoother with increasing gold plating thickness, thus resulting in smaller gaps and consequently higher gap conductance.

Evaluation of reliability and metallurgical integrity of wire bonds and lead free solder joints on flexible printed circuit board sample modules

This paper presents a study of the optimization of the gold plating thickness for the use of both wire bonding and soldered interconnects on a flexible printed circuit board sample module. Wire bondability is typically better, when the gold plating thickness is greater than 30 μin.; however, the risk of problems with solder joint embrittlement becomes a concern with thick gold plating. In order to better understand the effect of the gold plating thickness on wire bondability and solder joint embrittlement, an evaluation was performed on samples with three ranges of gold plating thicknesses (10–20 μin., 20–30 μin., and 30–45 μin.), on flexible printed circuit board (PCB), substrates. Mechanical shear testing and metallurgical analyses were conducted on chip component solder joints in this three thickness gold study. Thermal shock and drop testing were conducted to evaluate the reliability of the sample modules. Drop testing is especially critical for determining the reliability of the sample modules, which are used in portable consumer electronics products. Reliability testing and metallurgical analyses have been performed to characterize the effect of gold embrittlement on the mechanical integrity of the solder joints with a gold content ranging from 1 to 4 wt.%.

Investigation of weld cracking in Nd:yttrium–aluminum–garnet keyhole spot welding of materials used in optoelectronic packaging

The welding of a problematic optical device weld joint between dissimilar materials is investigated in depth. The original material combination of cold rolled steel 1010 with 6 μm of gold coating and 304 L produced consistent weld cracking. The CRS1010 material was fixed, however the other component was open to material selection. The materials tested were 304 L stainless steel, kovar, invar, and Carpenter high permeability 49 alloy. The effect of these different materials, laser pulse parameters, level of weld constraint, and thickness of gold plating on the CRS component are investigated to determine the key crack initiator. The results indicated that gold thickness is the key factor in the cracking mechanism, however weld volume and the level of weld constraint are also significant, with material selection a secondary factor. The use of pulse shaping had no effect on alleviating or reducing the extent of cracking.

Board level reliability of PBGA using flex substrate

Assurance of board level reliability is necessary and required for adopting any new packages into products. This paper presents board level reliability test results of a flex substrate BGA under thermal and bend cyclic tests. It is well known that solder joint reliability is affected by many factors, such as the size of chip, joint stand-off height, pad design, test board surface finish, substrate gold plating thickness and the utilization of underfill material, etc. However, most of the works have been conducted are BGA on rigid substrates. In this work, thermal cyclic test is performed to re-examine these factors using package housed on a flex substrate. Bending test with two deflections is also performed to investigate solder joint fatigue life and failure modes under mechanically repetitive loading.Two-parameter Weibull model is used to analyze joint fatigue life. Failure analysis is conducted and discussed for each case. Under temperature cycling test, chip size, polyimide thickness and underfill material utilization were found to have significant impacts on joint fatigue life, especially the effect of applying underfill material to the joint. Epoxy thickness was found to have little effect on the joint fatigue life for this case.The effects of test board surface finish and substrate gold plating thickness on the joint fatigue life were found coupled. The term “substrate” here refers to the chip carrier, while the “board” here refers to motherboard, which is the board to assemble test vehicles on. The gold thickness here all refers to the electrolytic gold plating on the substrate. Using organic solderability preservative boards, substrate gold plating thickness affects joint fatigue life slightly, but with Au–Ni test boards, the effect is tremendous. The difference is due to different intermetallic compounds (IMC) formed. In other words, different IMC systems are formed due to different combination of test board surface finish and substrate gold plating thickness. As a result, different IMC induces different failure modes. The joint fatigue life under cyclic bend test with different deflections is also probed and shown. The corresponding failure modes are also discussed.

A comparative assessment of gold plating thickness required for stationary electrical contacts

There is considerable interest in the corrosion control of thin gold plated contact surfaces of consumer electronics products. This originates in the desire to minimize the use of costly gold and other precious metals, like palladium, and their alloys, without sacrificing reliability. When the application is in adverse environments, gold plated contact finishes can enhance the reliability of the electrical contacts. However, the failure mechanisms depend strongly on the operating environment and contact plating and are time dependent processes. Numerous investigations on unloaded gold plated surfaces (unmated and tested at non-operating environmental condition) have been performed to simulate the contact failures induced by corrosion. However, no models have been proposed that account for the effects of loading electrically and mechanically on the corrosion process and selection of gold plating thickness. This article describes the study of loaded electrical contacts with the objective of setting up a comparative model between unloaded and loaded electrical contacts, which will improve the understanding of the influence of contact force and applied voltage on the selection of gold layer thickness and finish material. Contact force will improve the performance of gold finishes in stationary electrical contacts and decrease significantly, the gold plating thickness requirements compared to unloaded situation because of its effect on suppression of surface film growth. Voltage will accelerate the growth of surface film and result in the decrease of contact lifetime.

ＢＧＡパッケージ用テープ基板における無電解金めっき厚さとワイヤボンディング性およびはんだボール接合性

Tape carriers have been used as BGA substrates because of their thin, fine circuits and high manufacturing accuracy. Electroless gold plating on tape carriers has become required. Electroless gold plating tape carriers having good gold wire bondability and ball solderability are being developed. We studied the influence of electroless gold plating thickness on wire bondability and ball solderability, with the following results: (1) The pull strength of gold wires on tape carriers with 0.2μm and over gold plating thickness was 0.07N or more. (2) The shear strength of solder balls on tape carriers with 0.2μm and below gold plating thickness was 3N or more after heat aging at 150°C for 500h. (3) Tape carriers with 0.2μm gold plating film had good wire bondability and ball solderability.

XRF measurement of gold plating thickness

XRF measurement of gold plating thickness

An analytical investigation of seal ring solder voiding on IC packages

Seal ring voiding on solder sealed IC packages is discussed. Surface analysis data demonstrates that nickel oxide, which diffuses from an underlying nickel layer during high temperature processing, is a major cause of the seal ring solder voiding. Voids result from nonwelting of the solder to the gold plate due to the interference of the nickel oxide. A diffusion model is combined with kinetic data to predict nickel diffusion times as a function of gold plating thickness and processing conditions.

The Effect of Gold-Tin Intermetallic Compound on the Low Cycle Fatigue Behavior of Copper Alloy C72700 and C17200 Wires

Many connectors and springs fabricated from copper base spring materials require a gold-plated surface finish. Often such parts are joined or interconnected to the electronic package by soldering with tinlead solder. Upon application of heat, the gold plating may interact with the tin contained in the solder to produce a brittle intermetallic compound. Such a compound may adversely affect the fatigue resistance of the connector or spring. The effect of gold-tin intermetallic compound on the low cycle fatigue behavior of two high strength copper base alloys in wire form was studied. Alloys C72700 (Cu, 9 Ni, 6 Sn) and C17200 (Cu, 1.9 Be) in the form of 0.009-0.011 inch (229-279µm) diameter wires were gold plated using two techniques. Immersion plating was used to produce a gold plating thickness of 5-10 µinch (0.12-0.25 µm). Electroplating was used to produce a gold plating thickness of 30 µinch (0.75 µm) on a second sample lot. Tin-lead solder (60 Sn 40 Pb) was then electroplated over the gold. The samples were then heated to a temperature just slightly below the melting point of the solder to produce the desired surface layer of gold-tin intermetallic compound. Fatigue tests were made on a commercial wire fatigue tester which is based on the principle of a rotating Euler column. The fatigue data are presented in the form of Weibull probability distribution plots of the fatigue life, N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> at a given maximum bending stress level S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</inf> . The effect of either type of gold plating, gold and solder plating with and without intermetallic compound formation, on fatigue was studied. Immersion plating of gold had no effect on fatigue while electroplating caused a significant decrease in fatigue of the alloy wires studied. The formation of the gold-tin intermetallic compound caused a drastic decrease in fatigue life (by a factor of five to one). It is therefore recommended that every effort be made to eliminate or prevent the occurrence of the gold-tin intermetallic compound in critical areas where connector or spring surfaces are subjected to fatigue.

Some Quality Control Studies in the Fabrication of Mics

Many MIC subsystems like 2 GHz amplifiers, 6 and 7 GHz detectors are being produced in ITI. To achieve acceptable quality at reasonable yield level, it is essential to have in-process control on the quality of materials and processes. Studies conducted in this connection are reported in this paper. The performance of typical circuits like 2GHz-I0 dB coupler and a 7 GHz-10 dB coupler/detector have been studied with variation of (a) substrate thickness (b) line widths and (c) gold plating thickness. Evaluations have been conducted in the optimization of the gold bath parameters to achieve gold film of acceptable porosity and grain structure so as to minimize the degradation of adhesion in subsequent high temperatue assembly operations. Assembly of MIC's has been done using conductive silver epoxy, solder pastes of tin, lead and indium and also with gold-tin preforms. The results of above studies have been incorporated in our MIC fabrication line and have resulted in considerable improvement in the yield.

Production Control of Gold and Rhodium Plating Thickness on Very Small Samples by X-Ray Spectroscopy

AbstractManufacture of reed switches, critical components in present-day dataprocessing support devices, requires a means of accurate, rapid analysis of elements used in plating tlie levers of the switch. Because of gready reduced feedback time, X-ray spectroscopy has replaced metallographic sectioning and optical measurement as a plating-thickness control method. While 6 hr were required to obtain thickness data for a given sample size by sectioning, X-ray spectroscopy requires only 2 hr, which permits better control of the plating operating. X-ray spectroscopy is now used routinely to control both gold and rhodium plating thicknesses in the 20- to 100μin. (1 × 10−6) thickness range. The large number of samples prevents long count duration, while the small sample size (0.110 by 0.033 in.) reduces the precision of the analysis. However, the precision of the X-ray and optical methods is approximately the same, 8% variance. X-ray accuracy is comparable to that of sectioning since the standards are obtained by sectioning. Simplicity of operation is required since relatively untrained operators are used. An aperture system is used to reduce background. The rhodium thickness measurement is obtained from gross rhodium intensity. Attenuation of gross nickel intensity from the base material was found to be a better measure of gold thickness intensity. Calibration for hoth gold and rhodium is performed by using the same wide detector conditions. The choice of analysis is made by changing only the 2θ angle, thus avoiding the time required for recalibration when changing analysis.

Determination of Micro Rhodium Film Thickness and of Gold Plating Thickness on Printed Circuits by Beta Radiation Backscatter Measurements

Beta radiation backscatter techniques were applied to thickness measurements of gold plating on printed circuit cards and of very thin rhodium films vaporized on a sapphire crystalline base. Gold thicknesses between 100 to 500 mu cm were determined with an accuracy of 18 mu cm. Rhodium film thickness was measured from 0.5 to 5 mu cm with an accuracy of 0.5 mu cm. The method of analysis described is nondestructive and is designed to give sensitive and reliable results. (auth)