Technical Library | 2019-06-03 15:32:40.0
ACI Technologies was pleased to assist a customer by conducting elemental analysis on several assemblies displaying severe corrosion. Several board assemblies had failed in the field and exhibited areas of corrosion in close proximity to onboard components. The most common source of corrosion on electronic assemblies is residual flux. Fluxes are specific chemistries applied during the soldering process which improve the wetting of the solder to both the pad and component when forming the solder joint. They can be highly reactive chemicals that, if left on the assemblies, can lead to corrosion, electrical degradation, and decreased reliability. In the presence of moisture and electrical bias, flux residue can enable dendritic growth as a result of electrochemical migration (ECM).
Technical Library | 2020-03-09 10:50:17.0
A customer called the Helpline seeking advice for cleaning no-clean fluxes prior to applying a conformal coating. The customer's assemblies were manufactured with a no-clean rosin based solder paste (ROL0) and were cleaned with an isopropyl alcohol (IPA) wash. After cleaning, a white residue was sometimes found in areas with high paste concentrations and was interfering with the adhesion of the conformal coating (Figure 1). For conformal coatings to adhere properly, the printed circuit board (PCB) surface must be clean of fluxes and other residues. In addition, ionic contamination left by flux residues can lead to corrosion and dendrite growth, two common causes of electronic opens and shorts. Other residues can lead to unwanted impedance and physical interference with moving parts.
Technical Library | 2019-05-23 10:42:00.0
Why identify flux residues? The primary purpose of flux is to reduce species of metal oxides from solderable surfaces, and to act as a mechanism for lifting and removing debris. If the assembly is not properly cleaned after manufacturing, flux may continue to reduce metals and may eventually corrode the assembly. When the assembly is powered, the metal ions may precipitate along electromagnetic field lines and form dendritic shorts. In addition, the presence of residue can alter the insulation properties of a board, affect the adhesion of the conformal coating, or interfere with the moving parts of the assembly. In radio frequency (RF) applications, flux may change the RF properties on the surface of the printed circuit board (PCB) such as the dielectric strength, surface resistance, and Q-resonance.
Technical Library | 2023-04-17 17:05:47.0
In an ideal world, manufacturing devices would work all of the time, however, every company receives customer returns for a variety of reasons. If these returned parts contributed to a fail, most companies will perform failure analysis (FA) on the returned parts to determine the root cause of the failure. Failure can occur for a multitude of reasons, for example: wear out, fatigue, design issues, manufacturing flaw or defect. This information is then used to improve the overall quality of the product and prevent reoccurrence. If no defect is found, it is possible that in fact the product has no defect. On the other hand, the defect could be elusive and the FA techniques insufficient to detect said deficiency. No-clean flux residues can cause intermittent or elusive, hard to find defects. In an attempt to understand the effects of no-clean flux residues from the secondary soldering and cleaning processes, a matrix of varying process and cleaning operation was investigated. Of special interest, traveling flux residues and entrapped residues were examined, as well as localized and batch cleaning processes. Various techniques were employed to test the remaining residues in order to assess their propensity to cause a latent failure. These techniques include Surface Insulation Resistance1 (SIR) testing at 40⁰C/90% RH, 5 VDC bias along with C32 testing and Ion Exchange Chromatography (IC). These techniques facilitate the assessment of the capillary effect the tight spacing these component structures have when flux residues are present. It is expected that dendritic shorting and measurable current leakage will occur, indicating a failing SIR test. However, since the residue resides under the discrete components, there will be no visual evidence of dendritic growth or metal migration.
Technical Library | 2018-08-29 21:17:53.0
No-clean solder pastes are widely used in a number of applications that are exposed to wide variations in temperature during the life of the assembled electronics device. Some have observed that cracks can and do form in flux residue and have postulated that this is the result of or exacerbated by temperature cycling. Furthermore, the potential exists for the flux residue to soften or liquefy at elevated temperatures, and even flow if orientated parallel to gravity. In situations such as in automotive electronics, where significant temperature cycling is a reality and high reliability is a must, concern sometimes exists that the cracking and possible softening or liquefying of the residue may have a deleterious effect on the electrical reliability of the flux residue. This paper will attempt to address this concern.
Technical Library | 2017-02-09 17:08:44.0
The SMT assembly world, especially within the commercial electronics realm, is dominated by no-clean solder paste technology. A solder paste flux residue that does not require removal is very attractive in a competitive world where every penny of assembly cost counts. One important aspect of the reliability of assembled devices is the nature of the no-clean solder paste flux residue. Most people in this field understand the importance of having a process that renders the solder paste flux residue as benign and inert as possible, thereby ensuring electrical reliability.But, of all the factors that play into the electrical reliability of the solder paste flux residue, is there any impact made by the age of the solder paste and how it was stored? This paper uses J-STD-004B SIR (Surface Insulation Resistance) testing to examine this question.
Technical Library | 2015-02-27 16:46:30.0
During the last period of newly assembled electrical devices (pcbs), new component types like LGA and QFN were also qualified as well as smaller passive components with reliability requirements based on the automotive and industrial industry. In the narrow gaps under components, residues can accumulate more by the capillary forces. This is not that much a surface resistance than an interface issue. Also that the flux residues under such types of components creates interaction with the solder resists from the pcb, as well as the component body was not completely described in the standard SIR measurement. On the other hand also, electrical influence with higher voltage creates new terms and conditions, in particular the combination of power and logic in such devices. The standard SIR measurement cannot analyze those combinations.The paper will discuss the requirements for a measurement process, and will give results. The influences of the pcb and component quality will also be discussed. Furthermore it will describe requirements for nc solder paste to increase the chemical/thermical/electrical reliability for whole devices
Technical Library | 2017-05-17 22:33:43.0
The selective soldering application requires a combination of performance attributes that traditional liquid fluxes designed for wave soldering applications cannot fulfill. First, the flux deposition on the board needs to be carefully controlled. Proper fine tuning of the flux physicochemical characteristics combined with a process optimization are mandatory to strike the right balance between solderability and reliability. However, localization of the flux residue through the drop jet process is not enough to guarantee the expected performance level. The flux needs to be designed to minimize the impact of unavoidable spreading and splashing events.From this perspective a fundamental understanding of the relationships between formulation and reliability is critical. In this application, thermal history of the flux residues (from room temperature to solder liquidus) is a key performance driver. Finally, it is necessary to conduct statistically designed experiments on industrial selective soldering machines in order to map the relationships between flux characteristics and selective process friendliness.
Technical Library | 1999-05-07 10:47:00.0
White residue remaining after cleaning circuit board assemblies can be caused by a variety of chemicals and reactions. Rosin and water-soluble fluxes, circuit board resins and epoxies, component materials and other contamination all contribute to this complex chemistry. This paper discusses many of the sources of the residues that seem to be an ever-increasing occurrence.
Technical Library | 2018-11-20 21:33:57.0
There are several industry-accepted methods for determining the reliability of flux residues after assembly. The recommended methods of test sample preparation do not always closely mimic the thermal cycle experienced by an assembly. Therefore, extraction from actual assemblies has become a popular method of process control to assess consistency of post-reflow cleanliness. Every method of post-reflow flux residue characterization will depend on the reflow process followed to prepare the coupon.This investigation will focus on the effect of thermal conditions on the remainder of active ingredients in flux residues after assembly with no-clean solder pastes.
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