Pb-Free Process Development for a High End Storage Area Network Application

2007 ◽  
Author(s):  
Sunil Gopakumar ◽  
Francois Billaut ◽  
Eric Fremd ◽  
Manthos Economou
Keyword(s):  
Thermal Cycling ◽  
Cycling Performance ◽  
Lead Free ◽  
Process Window ◽  
Successful Implementation ◽  
Soldering Process ◽  
Wave Soldering ◽  
Free Process ◽  
Plated Through Hole ◽  
The Impact

Lead free solders are being increasingly used in the electronic industry. While most of the electronic products, in terms of volume, are already built lead free, sectors of the industry including high end servers, networking and telecommunications are covered by “lead in solder” exemptions. It is unknown at this point how long these exemptions will last. In addition, many components such as memories have started appearing only in the Pb-free version. As a result, the industry has been pushed to either adopt a mixed assembly process or to transition early to a full Pb-free process. Even though numerous papers have outlined the successful implementation of a Pb-free process, few of them have actually looked at complex high-end multilayer boards in its entirety. This paper focuses on the issues involved in developing an acceptable Pb-free process window for thick, multilayer boards for SMT, Wave soldering, Rework and Press-fit operations. A laminate capable of withstanding Pb-free soldering temperatures was used to construct a 125-mil thick multilayer board with 18 layers which included 8 ground and 10 signal planes. This experiment utilized two popular Pb-free finishes commonly used in the industry: Immersion Silver and high temperature Organic Solderability Preservative (OSP). The widespread SAC 305 alloy with a composition of Sn3.0Ag0.5Cu was used for both SMT and wave soldering. Three sets of assemblies were built: Pb-free, Mixed and Sn/Pb. The mixed assembly mostly used Pb-free components with Sn/Pb solder paste. The impact of increased soldering temperatures on the board, components and reliability of the product were also studied as a part of this research endeavor. Board level reliability tests were conducted by subjecting the boards from 0°C to 100°C Air-to-Air thermal cycling as well as mechanical shock and vibration tests. A suite of reliability and destructive physical analysis (DPA) tests were carried out to establish the quality of the soldering using the eutectic Sn/Pb assembly as the baseline. The study compared the cycling performance of the three sets of assemblies and also looked at the potential impacts of moving to mixed assemblies. Results indicated a reduced process window for Pb-free, especially for the Pb-free wave soldering process due to reduced wetting of the plated through hole barrels as compared to Sn/Pb wave soldering process. The thermal cycling performance of the three sets of assemblies was found to be equivalent after 6000 cycles.

Transient Thermal Stress Analysis of a Plated Through Hole Subjected to Wave Soldering

1991 ◽  
Vol 113 (2) ◽  
pp. 149-155 ◽  
Author(s):  
D. Barker ◽  
M. Pecht ◽  
A. Dasgupta ◽  
S. Naqvi
Keyword(s):  
Thermal Stress ◽  
Stress Analysis ◽  
Three Dimensional ◽  
Strain History ◽  
Thermal Stress Analysis ◽  
Soldering Process ◽  
Wave Soldering ◽  
Plated Through Hole ◽  
The Impact ◽  
Through Hole

During a typical wave soldering operation a plated through hole (PTH) is exposed to temperatures which are higher than any rated operating temperatures. Understanding the heat transfer and the potential PTH damage mechanisms, which arise during the wave soldering process, is critical to PTH quality control and reliability. In particular, cracks may be initiated during the wave soldering transient and become manifest only after operational cycling. This paper presents a transient nonlinear thermal stress analysis of a nonsolder filled PTH that is subjected to a typical wave soldering process. A full three-dimensional orthotropic analysis and an axisymmetric analysis with cylindrically anisotropic properties are used and the results compared. Temperature and stress/strain history curves are examined to determine the impact of the wave soldering operation on the PTH fatigue life. The effect of PWB innerplanes on the PTH maximum stress and strain is also investigated.

Thermal decomposition of solder flux activators under simulated wave soldering conditions

2017 ◽  
Vol 29 (3) ◽  
pp. 133-143 ◽  
Author(s):  
Kamila Piotrowska ◽  
Morten Stendahl Jellesen ◽  
Rajan Ambat
Keyword(s):  
Thermal Treatment ◽  
Heat Exposure ◽  
Copper Surface ◽  
Substrate Material ◽  
Content Type ◽  
Soldering Process ◽  
Wave Soldering ◽  
Solder Flux ◽  
Solder Mask ◽  
The Impact

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.

An Investigation of the Lead-Free Surface Mount Soldering Process: Solder Joint Evaluation and Process Optimisation

2004 ◽  
Author(s):  
Claire Ryan ◽  
Jeff M. Punch ◽  
Bryan Rodgers ◽  
Greg Heaslip ◽  
Shane O’Neill ◽  
...  
Keyword(s):  
Screen Printing ◽  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Paste ◽  
Surface Mount ◽  
Snagcu Solder ◽  
Soldering Process ◽  
Free Process ◽  
Free Solder

A European Union ban on lead in most electrical and electronic equipment will be imposed as of July 1st 2006. The ban, along with market pressures, means that manufacturers must transfer from a tin-lead soldering process to a lead-free process. In this paper the implications on the surface mount (SMT) soldering process are presented. A set of experiments was conducted to investigate the screen-printing and reflow steps of the SMT process using a tin-silver-copper (95.5Sn3.8Ag0.7Cu) solder and a baseline of standard tin-lead (63Sn37Pb). 10×10 arrays of micro Ball Grid Array (micro-BGA) components mounted on 8-layer FR4 printed wiring boards (PWBs) were used. The screen-printing experiment addressed the deposition of the solder paste on the board. The parameters used in the investigation were print speed, squeegee pressure, snap-off distance, separation speed and cleaning interval, with the responses being measurements of paste height and volume. Optimum screen-printer settings were determined which give adequate paste volume and height and a good print definition. The reflow experiment investigated the following parameters of the temperature profile: preheat, soak, peak and cool down temperatures, and conveyor speed. The resulting solder joints were evaluated using cross-section analysis and x-ray techniques in order to determine the presence of defects. A mechanical fatigue test was also carried out in order to compare the strength of the solder joints. The overall quality of the lead-free solder joints was determined from these tests and compared to that of tin-lead. The outcome is a set of manufacturing guidelines for transferring to lead-free solder including optimum screen-printer and reflow oven settings for use with an SnAgCu solder.

Thermal decomposition of binary mixtures of organic activators used in no-clean fluxes and impact on PCBA corrosion reliability

2019 ◽  
Vol 32 (2) ◽  
pp. 93-103
Author(s):  
Kamila Piotrowska ◽  
Feng Li ◽  
Rajan Ambat
Keyword(s):  
Binary Mixture ◽  
Binary Mixtures ◽  
Proper Time ◽  
Scanning Calorimetry ◽  
Binary Blends ◽  
Content Type ◽  
Soldering Process ◽  
Wave Soldering ◽  
Decomposition Behavior ◽  
The Impact

Purpose The purpose of this paper is to investigate the decomposition behavior of binary mixtures of organic activators commonly used in the no-clean wave flux systems upon their exposure to thermal treatments simulating wave soldering temperatures. The binary blends of activators were studied at varying ratios between the components. Design/methodology/approach Differential scanning calorimetry and thermogravimetric analysis were used to study the characteristics of weak organic acid (WOA) mixtures degradation as a function of temperature. The amount of residue left on the surface after the heat treatments was estimated by gravimetric measurements as a function of binary mixture type, temperature and exposure time. Ion chromatography analysis was used for understanding the relative difference between decomposition of activators in binary blends. The aggressivity of the left residue was assessed using the acidity indication gel test, and effect on reliability was investigated by DC leakage current measurement performed under varying humidity and potential bias conditions. Findings The results show that the typical range of temperatures experienced by electronics during the wave soldering process is not sufficient for the removal of significant activator amounts. If the residues contain binary mixture of WOAs, the final ratio between the components, the residue level and the corrosive effects depend on the relative decomposition behavior of individual components. Among the WOA investigated under the conventional wave soldering temperature, the evaporation and removal of succinic acid is more dominant compared to adipic and glutaric acids. Practical implications The findings are attributed to the chemistry of WOAs typically used as flux activators for wave soldering purposes. The results show the importance of controlling the WOA content and ratio between activating components in a flux formulation in relation to its tendencies for evaporation during soldering and the impact of its residues on electronics reliability. Originality/value The results show that the significant levels of flux residues can only be removed at significantly higher temperatures and longer exposure times compared to the conventional temperature range used for the wave soldering process. The potential corrosion issues related to insufficient flux residues removal will be determined by the residue amount, its composition and ratio between organic components. The proper time of thermal treatment and careful choice of fluxing formulation could ensure more climatically reliable product.

Stitch-Bond-Shearing in Optoelectronic Devices, Caused by Lead-Free-Wave-Soldering – Do We Need Improved Wire-Bonding Methods?

2008 ◽  
Author(s):  
Peter Jacob ◽  
Michael Rütsch
Keyword(s):  
Optoelectronic Devices ◽  
Wire Bonding ◽  
Lead Free ◽  
System Level ◽  
Process Window ◽  
Free Wave ◽  
Reliability Problem ◽  
Wave Soldering ◽  
Level Process

Abstract This case study shows a typical example of a manufacturing-chain-induced reliability problem. All participants of the chain do their work within specifications, but, looking at the system level, severe reliability problems have been observed. In order to get back into the system-level process window, several corrective actions are possible. In this case, the most promising approach is an improvement of the stitch bond robustness, combined with a clear user specification.

Development of lead-free wave soldering process

2002 ◽  
Vol 25 (4) ◽  
pp. 289-299 ◽  
Author(s):  
M. Arra ◽  
D. Shangguan ◽  
S. Yi ◽  
R. Thalhammer ◽  
H. Fockenberger
Keyword(s):  
Lead Free ◽  
Free Wave ◽  
Soldering Process ◽  
Wave Soldering

Effects of Corner/Edge Bonding and Underfill Properties on the Thermal Cycling Performance of Lead Free Ball Grid Array Assemblies

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
P. Borgesen ◽  
D. Blass ◽  
M. Meilunas
Keyword(s):  
Thermal Cycling ◽  
Flip Chip ◽  
Printed Circuit Board ◽  
Ball Grid Array ◽  
Cycling Performance ◽  
Circuit Board ◽  
Lead Free ◽  
Sac305 Solder ◽  
Solder Balls ◽  
Selection Of

Underfilling will almost certainly improve the performance of an area array assembly in drop, vibration, etc. However, depending on the selection of materials, the thermal fatigue life may easily end up worse than without an underfill. This is even more true for lead free than for eutectic SnPb soldered assemblies. If reworkability is required, the bonding of the corners or a larger part of the component edges to the printed circuit board (PCB), without making contact with the solder joints, may offer a more attractive materials selection. A 30 mm flip chip ball grid array (FCBGA) component with SAC305 solder balls was attached to a PCB and tested in thermal cycling with underfills and corner/edge bonding reinforcements. Two corner bond materials and six reworkable and nonreworkable underfills with a variety of mechanical properties were considered. All of the present underfills reduced the thermal cycling performance, while edge bonding improved it by up to 50%. One set of the FCBGAs was assembled with a SnPb paste and underfilled with a soft reworkable underfill. Surprisingly, this improved the thermal cycling performance slightly beyond that of the nonunderfilled assemblies, providing up to three times better life than for those assembled with a SAC305 paste.

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