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1 – 10 of over 1000
Article
Publication date: 1 March 1993

M.E. Jozefowicz and N.‐C. Lee

The IPC‐SF‐818 surface insulation resistance (SIR) test data taken with the use of a variety of halide‐free, no‐clean fluxes are analysed against Bellcore TR‐NWT‐000078…

Abstract

The IPC‐SF‐818 surface insulation resistance (SIR) test data taken with the use of a variety of halide‐free, no‐clean fluxes are analysed against Bellcore TR‐NWT‐000078 electromigration (EM) test data. Neither test results show correlation with bulk flux resistivity, flux water extract resistivity, flux residue moisture pick‐up, and flux corrosivity without bias. However, in the case of rosin fluxes, the insulation resistance behaviour in both SIR and EM tests is a function of the pH value of fluxes. This phenomenon is more significant in the SIR test. In the case of low‐residue, no‐clean fluxes, only the SIR test displays such a pH dependent relationship. Data suggest that the 50 volts bias voltage used in the SIR test may be responsible for this, and can be explained with a high‐bias‐voltage‐induced electrolysis mechanism which is further promoted by a high pH environment. This failure mechanism is absent in the EM test which utilises 10 volts bias voltage, and probably will not occur under the normal 5 volts application conditions. Overall, the SIR test seems to be more stringent while the EM test appears to be more realistic.

Details

Circuit World, vol. 19 no. 4
Type: Research Article
ISSN: 0305-6120

Article
Publication date: 1 December 1996

P.T. Vianco and A.C. Claghorn **

A study was performed which investigated the wettability of 63Sn‐37Pb and 96.5Sn‐3.5Ag solders oncopper and gold ‐nickel plated Kovar ™ using a rosin ‐based, mildlyactivated (RMA…

228

Abstract

A study was performed which investigated the wettability of 63Sn‐37Pb and 96.5Sn‐3.5Ag solders on copper and gold ‐nickel plated Kovar ™ using a rosin ‐based, mildly activated (RMA) flux, a water soluble organic acid flux (WS ),and a low residue (LR) flux. The quantitative metric was the contact angle, θc, measured by the meniscometer /wetting balance technique. The first part of the study (Part 1) examined wetting performance following continuous exposure to 25°C prior to testing. Then, a preheating step was introduced into the experimental procedure after flux application, but preceding the actual wettability test in order to simulate a factory reflow process; these results are presented in Part II of this study. Contact angles for the 63Sn‐37Pb solder (215°C) on copper were 22±2° with the RMA flux, 12±5° for the WS flux, and 31±6° for the LR flux. Increasing the 63Sn‐37Pb solder temperature to 245°C improved wettability with the RMA and LR fluxes, but no change was observed with the WS fulx. Theii 96.5Sn‐3.5Ag lead ‐free solder exhibited poorer wettability on copper compared with the 63Sn‐37Pb alloy, with contact angles of 41±2° (RMA), 63±15°(WS) and 39±4°(LR). For the gold ‐nickel plated Kovar™ substrates, the 63Sn‐37Pb solder at 215° had contact angles of 15±3°, 35±6° and 29±6° for the RMA, WS and LR fluxes, respectively. The values were reduced at the higher test temperature (245°). The 96.5Sn‐3.5Ag solder also exhibited good wetting performance on the gold ‐nickel plated Kovar™ specimens compared with copper. Analysis of the interfacial tension parameters, γSF‐γSLand γLF ,exemplified the importance of γLF as well as the condition of the surfaces (γSF ) on wettability performance. A so ‐called ‘combined analysis’ of the 63Sn‐37Pb and 96.5Sn‐3.5Ag wettability data on either copper or gold ‐ nickel plated Kovar™ substrates was used to predict the solder temperature dependence of wettability for the three fluxes and two base materials.

Details

Soldering & Surface Mount Technology, vol. 8 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 August 1999

William Casey

The rapid progress of ball grid array (BGA) component technology has served to alleviate many problems associated with the placement and soldering of high lead count, fine pitch…

Abstract

The rapid progress of ball grid array (BGA) component technology has served to alleviate many problems associated with the placement and soldering of high lead count, fine pitch surface mount technology (SMT) packages. An unfortunate result of this process, however, is the occurrence of voids in the interconnecting eutectic solder balls of these packages. Large voids can affect the mechanical and thermal properties of the interconnect, which can reduce a component’s mean time‐to‐failure and may also affect the transmission of high frequency electrical signals through the solder ball. For this reason, several experiments were conducted to investigate the manner and mechanisms in which voids are introduced into eutectic BGA solder ball joints. The following process parameters were found to be the primary parameters responsible for the voiding phenomenon: condition of the component’s alloy and substrate, oxygen concentration in the reflow atmosphere, solder paste properties and the reflow profile. Through modification and optimization of process parameters in the manufacturing environment, BGA solder joint voiding was greatly reduced.

Details

Soldering & Surface Mount Technology, vol. 11 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 March 1995

S.V. Vasan, P.T. Truong and G. Dody

This paper discusses chip removal and replacement processes of flip chip assemblies (FCAs) on printed wiring boards (PWBs). The original chip connection is achieved via mass…

Abstract

This paper discusses chip removal and replacement processes of flip chip assemblies (FCAs) on printed wiring boards (PWBs). The original chip connection is achieved via mass reflow as in a surface mount assembly process. The FCA interconnection is one involving a surrogate solder bump on a chip and a lower melt solder on the PWB pads that fuses with the bump during reflow. The chip removal process thus entails melting the lower melt solder locally using hot gas. The following considerations will be discussed in the paper: chip size, chip removal methodology, local vs mass reflow for replacement attachment, solder height, the impact of multiple reflows on the solder joint integrity of assemblies. The use of the flip chip rework machine to remove ball grid arrays (BGAs) and quad flatpacks (QFPs) will be briefly addressed.

Details

Circuit World, vol. 21 no. 3
Type: Research Article
ISSN: 0305-6120

Content available
Article
Publication date: 1 April 2001

Brian Ellis

206

Abstract

Details

Soldering & Surface Mount Technology, vol. 13 no. 1
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 January 1990

M.A. Nasta, G.R. Hill and D. Campbell

The filterable particles found in electronic solder fluxes vary considerably in both concentration and chemistry. Four fluxes from three manufacturers were examined, including…

Abstract

The filterable particles found in electronic solder fluxes vary considerably in both concentration and chemistry. Four fluxes from three manufacturers were examined, including both rosin fluxes and mildly activated resin fluxes. Individual particles were examined by optical light microscopy (OLM) and scanning electron microscopy/energy dispersive X‐ray spectroscopy (SEM/EDX). Finally, an automated SEM/EDX system was used to collect and summarise information about the size and chemistry of a hundred or more particles from each flux. The number of particles per microgram of flux was found to vary by two orders of magnitude (0.004 to 0.4 per μg). The particle diameters ranged from 0.2–20 μm with averages of 1–3 μm. A large fraction of the particles (33–75% by number) were organic substances not soluble in the flux. The bulk of the inorganic particles were composed of sulphates, silicates and metal oxides. Thus, some solder fluxes may be introducing several contaminant particles into each solder contact. These contaminants may affect the quality of the solder joint depending on particle size and composition.

Details

Soldering & Surface Mount Technology, vol. 2 no. 1
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 July 2006

Deepak Manjunath, Satyanarayan Iyer, Shawn Eckel, Purushothaman Damodaran and Krishnaswami Srihari

The leaching of lead from electronic components in landfills to ground water is harmful to health and to the environment. Increasing concern over the use of lead in electronics…

Abstract

Purpose

The leaching of lead from electronic components in landfills to ground water is harmful to health and to the environment. Increasing concern over the use of lead in electronics manufacturing has led to legislation to restrict its use as a joining material. Consequently, significant recent research efforts have been geared to identification of suitable lead‐free solder pastes. Typically, lead‐free solder pastes contain a very active flux in an effort to improve wetting. These aggressive fluxes have the tendency to explode (or burst) and create flux spatter, causing many process problems with sensitive electronic components. The purpose of this paper is to propose solution procedures to minimize/eliminate these flux spatters, particularly, on gold fingers in memory modules when lead‐free solder pastes are used.

Design/methodology/approach

Four no‐clean, lead‐free Sn‐Ag‐Cu (SAC) alloy‐based solder pastes consisting of four different flux systems from three different vendors were evaluated. Two types of reflow profiles (linear and ramp‐soak‐ramp) were also evaluated. Experiments were also conducted to optimise the soak temperature and soak time to determine a broader process window for lead‐free volume production with minimal flux spatter on the contact fingers of memory modules. In order to validate our findings the recommended profile and paste was adopted in production. Additional experiments on a board with a different surface finish were also carried out to validate the recommendations.

Findings

Flux spatter can be reduced/eliminated through proper selection of flux chemistry and reflow profile optimisation. The experimental study conducted indicates there is a reduction in the occurrence of flux spatter when a ramp‐soak‐ramp profile is used with lead‐free solder pastes.

Originality/value

Demonstrates that flux spatter can be reduced/eliminated by carefully choosing a soak profile and appropriate flux chemistry.

Details

Soldering & Surface Mount Technology, vol. 18 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 7 September 2015

Vadimas Verdingovas, Morten Stendahl Jellesen and Rajan Ambat

This paper aims to investigate the effect of no-clean flux chemistry with various weak organic acids (WOAs) as activators on the corrosion reliability of electronics with emphasis…

Abstract

Purpose

This paper aims to investigate the effect of no-clean flux chemistry with various weak organic acids (WOAs) as activators on the corrosion reliability of electronics with emphasis on the hygroscopic nature of the residue.

Design/methodology/approach

The hygroscopicity of flux residue was studied by quartz crystal microbalance, while corrosive effects were studied by leakage current and impedance measurements on standard test boards. The measurements were performed as a function of relative humidity (RH) in the range from 60 to ∼99 per cent at 25°C. The corrosiveness of solder flux systems was visualized by the ex situ analysis using a gel with tin ion indicator.

Findings

The results showed that the solder flux residues are characterized by different threshold RH, above which a sudden increase in direct current leakage by 2–4 orders of magnitude and a significant reduction in surface resistance in the impedance measurements were observed.

Practical implications

The findings are attributed to the deliquescence RH of the WOA(s) in the flux and chemistry of water-layer formation. The results show the importance of WOA type in relation to its solubility and deliquescence RH on the corrosion reliability of printed circuit boards under humid conditions.

Originality/value

The classification of solder flux systems according to IPC J-STD-004 standard does not specify the WOAs in the flux; however, ranking of the flux systems based on the hygroscopic property of activators would be useful information when selecting no-clean flux systems for electronics with applications in humid conditions.

Details

Soldering & Surface Mount Technology, vol. 27 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 March 1995

E.M. Oh

PCB manufacturers are switching from the use of RMA fluxes in their soldering and rework processes to low residue type (i.e., ‘no‐clean’) fluxes. Unfortunately, successful…

Abstract

PCB manufacturers are switching from the use of RMA fluxes in their soldering and rework processes to low residue type (i.e., ‘no‐clean’) fluxes. Unfortunately, successful changeover is not simply a matter of substituting a no‐clean into an existing RMA process. Soldering process parameters must change, necessitating an understanding of the interplay between flux chemistry and heat delivery. Higher temperatures can result in an effective decrease in the concentration of the active fluxing agents. Also, data show a decrease in the inherent wetting force of a no‐clean flux with increasing temperature. These two factors reduce fluxing action below the rate of oxidation occurring at the solder connection and the soldering iron tip. These can lead to incomplete surface cleaning and inefficient heat transfer, resulting in poorly soldered connections. Lower solder joint defect rates are obtained with no‐clean solders and fluxes when soldering temperatures are reduced to a minimum.

Details

Soldering & Surface Mount Technology, vol. 7 no. 3
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 5 June 2017

Kamila Piotrowska, Morten Stendahl Jellesen and Rajan Ambat

The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue…

Abstract

Purpose

The aim of this work is to investigate the decomposition behaviour of the activator species commonly used in the wave solder no-clean flux systems and to estimate the residue amount left after subjecting the samples to simulated wave soldering conditions.

Design/methodology/approach

Changes in the chemical structure of the activators were studied using Fourier transform infrared spectroscopy technique and were correlated to the exposure temperatures within the range of wave soldering process. The amount of residue left on the surface was estimated using standardized acid-base titration method as a function of temperature, time of exposure and the substrate material used.

Findings

The study shows that there is a possibility of anhydride-like species formation during the thermal treatment of fluxes containing weak organic acids (WOAs) as activators (succinic and DL-malic). The decomposition patterns of solder flux activators depend on their chemical nature, time of heat exposure and substrate materials. Evaporation of the residue from the surface of different materials (laminate with solder mask, copper surface or glass surface) was found to be more pronounced for succinic-based solutions at highest test temperatures than for adipic acid. Less left residue was found on the laminate surface with solder mask (∼5-20 per cent of initial amount at 350°C) and poorest acid evaporation was noted for glass substrates (∼15-90 per cent).

Practical implications

The findings are attributed to the chemistry of WOAs typically used as solder flux activators. The results show the importance WOA type in relation to its melting/boiling points and the impact on the residual amount of contamination left after soldering process.

Originality/value

The results show that the evaporation of the flux residues takes place only at significantly high temperatures and longer exposure times are needed compared to the temperature range used for the wave soldering process. The extended time of thermal treatment and careful choice of fluxing technology would ensure obtaining more climatically reliable product.

Details

Soldering & Surface Mount Technology, vol. 29 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 10 of over 1000