Technical Library | 2017-12-11 22:31:06.0
Typical printed circuit board assemblies (PCBAs) processed by reflow, wave, or selective wave soldering were analysed for typical levels of process related residues, resulting from a specific or combination of soldering process. Typical solder flux residue distribution pattern, composition, and concentration are profiled and reported. Presence of localized flux residues were visualized using a commercial Residue RAT gel test and chemical structure was identified by FT-IR, while the concentration was measured using ion chromatography, and the electrical properties of the extracts were determined by measuring the leak current using a twin platinum electrode setup. Localized extraction of residue was carried out using a commercial C3 extraction system. Results clearly show that the amount and distribution of flux residues are a function of the soldering process, and the level can be reduced by an appropriate cleaning. Selective soldering process generates significantly higher levels of residues compared to the wave and reflow process. For conformal coated PCBAs, the contamination levels generated from the tested wave and selective soldering process are found to be enough to generate blisters under exposure to high humidity levels.
Technical Library | 2023-04-17 21:17:59.0
The purpose of this paper is to evaluate and compare the effectiveness and sensitivity of different cleanliness verification tests for post soldered printed circuit board assemblies (PCBAs) to provide an understanding of current industry practice for ionic contamination detection limits. Design/methodology/approach – PCBAs were subjected to different flux residue cleaning dwell times and cleanliness levels were verified with resistivity of solvent extract, critical cleanliness control (C3) test, and ion chromatography analyses to provide results capable of differentiating different sensitivity levels for each test. Findings – This study provides an understanding of current industry practice for ionic contamination detection using verification tests with different detection sensitivity levels. Some of the available cleanliness monitoring systems, particularly at critical areas of circuitry that are prone to product failure and residue entrapment, may have been overlooked. Research limitations/implications – Only Sn/Pb, clean type flux residue was evaluated. Thus, the current study was not an all encompassing project that is representative of other chemistry-based flux residues. Practical implications – The paper provides a reference that can be used to determine the most suitable and effective verification test for the detection of ionic contamination on PCBAs. Originality/value – Flux residue-related problems have long existed in the industry. The findings presented in this paper give a basic understanding to PCBA manufacturers when they are trying to choose the most suitable and effective verification test for the detection of ionic contamination on their products. Hence, the negative impact of flux residue on the respective product's long-term reliability and performance can be minimized and monitored effectively.
Technical Library | 2017-07-27 16:51:57.0
Reliability Expectations of Highly Dense Electronic Assemblies is commonly validated using Ion Chromatography and Surface Insulation Resistance. Surface Insulation Resistance tests resistance drops on both cleaned and non-cleaned circuit assemblies. It is well documented in the literature that SIR detects ionic residue and the potential of this residue to cause leakage currents in the presence of humidity and bias. Residues under leadless components are hard to inspect for and to ensure flux residue is totally removed. The question many assemblers consider is the risk of residues that may still be present under the body of components.
Technical Library | 2023-05-22 16:49:42.0
Our customers' issues • Apertures are getting smaller • Paste does not release as well • Contaminates the bottom of the stencil • Increases defects / reduces yield Insufficient solder Bridging Solder balls on surface of PCB Flux residue • Requires more frequent cleaning • Reduced efficiency (wasted time) • Increased use of consumables (cost) USC fabric (use "cheap" fabric to reduce cost) Lint creates more defects Cleaning chemistries (use IPA to reduce cost) IPA breaks down flux and can create more defects
Technical Library | 2023-06-12 18:33:29.0
This paper presents a real-time predictive approach to improve solder paste stencil printing cycle decision making process in surface mount assembly lines. Stencil cleaning is a critical process that influences the quality and efficiency of printing circuit board. Stencil cleaning operation depends on various process variables, such as printing speed, printing pressure, and aperture shape. The objective of this research is to help efficiently decide stencil printing cleaning cycle by applying data-driven predictive methods. To predict the printed circuit board quality level, a recurrent neural network (RNN) is applied to obtain the printing performance for the different cleaning aging. In the prediction model, not only the previous printing performance statuses are included, but also the printing settings are used to enhance the RNN learning. The model is tested using data collected from an actual solder paste stencil printing line. Based on the predicted printing performance level, the model can help automatically identify the possible cleaning cycle in practice. The results indicate that the proposed model architecture can predictively provide accurate solder paste printing process information to decision makers and increase the quality of the stencil printing process.
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 | 2016-09-08 16:27:49.0
In this investigation a test matrix was completed utilizing 900 electrodes (small circuit board with parallel copper traces on FR-4 with LPI soldermask at 6, 10 and 50 mil spacing): 12 ionic contaminants were applied in five concentrations to three different spaced electrodes with five replicas each (three different bare copper trace spacing / five replications of each with five levels of ionic concentration). The investigation was to assess the electrical response under controlled heat and humidity conditions of the known applied contamination to electrodes, using the IPC SIR (surface insulation resistance) J-STD 001 limits and determine at what level of contamination and spacing the ionic / organic residue has a failing effect on SIR.
Technical Library | 2023-02-13 18:56:42.0
This paper describes the results of an intensive whisker formation study on Pb-free assemblies with different levels of cleanliness. Thirteen types of as-received surface-mount and pin-through-hole components were cleaned and intentionally contaminated with solutions containing chloride, sulfate, bromide, and nitrate. Then the parts were assembled on double-sided boards that were also cleaned or intentionally contaminated with three fluxes having different halide contents. The assemblies were subjected to high-temperature/high-humidity testing (85_C/85% RH). Periodic examination found that contamination triggered whisker formation on both exposed tin and solder fillets. Whisker occurrence and parameters depending on the type and level of contamination are discussed. Cross-sections were used to assess the metallurgical aspects of whisker formation and the microstructural changes occurring during corrosion.
Technical Library | 2017-07-13 16:16:27.0
Controlled humidity and temperature controlled surface insulation resistance (SIR) measurements of flux covered test vehicles, subject to a direct current (D.C.) bias voltage are recognized by a number of global standards organizations as the preferred method to determine if no clean solder paste and wave soldering flux residues are suitable for reliable electronic assemblies. The IPC, Japanese Industry Standard (JIS), Deutsches Institut fur Normung (DIN) and International Electrical Commission (IEC) all have industry reviewed standards using similar variations of this measurement. (...) This study will compare the results from testing two solder pastes using the IPC-J-STD-004B, IPC TM-650 2.6.3.7 surface insulation resistance test, and IPC TM-650 2.3.25 in an attempt to investigate the correlation of ROSE methods as predictors of electronic assembly electrical reliability.
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.
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