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Summarizes the different techniques for the removal of conformal coatings from printed circuit boards and other electronic assemblies. Addresses each of the four techniques for the removal of conformal coating (thermal, mechanical, chemical and abrasive), along with how they work with each type of conformal coating (urethane, acrylic, silicone, epoxy, parylene and UV curable coatings). Also provides summaries for the removal times and clean up for each technique.

The purpose of this paper is to study the effect of conformal coating on the thermal cycling reliability of anisotropically conductive adhesive film (ACF) joined flip chip components on FR‐4 and polyimide (PI) substrates.

Test chips were joined using flip chip technology and an anisotropically conductive adhesive. The conformal coating used was parylene C and it was applied using the vapour deposition polymerisation method. The reliability of ACF joined flip chip components on FR‐4 and PI substrates was evaluated using −40/+85°C thermal cycling testing. Test lots with and without parylene C coating were studied. Additionally, one test lot with initial moisture inside the coating layer and a PI substrate was subjected to the test. The reliability results were analyzed using Weibull analysis and failure analysis was performed to study the failure mechanisms using cross sectioning and optical and scanning electron microscopy.

The results show a clear difference between the FR‐4 and PI substrate materials. PI substrate material proved to be reliable enough to withstand the thermal cycling testing. Two different occurrences of the first failures are seen and analyzed with FR‐4 substrates. The conformal coating layer did not seem to impair the reliability. Parylene C coating proved to be a reliable choice to protect, and even improve, the thermal cycling reliability of flip chip devices.

Usually, conformal coatings are studied in humidity tests. However, it is also vital to know whether the conformal coatings affect the reliability in thermal cycling and there is a lack of reliability studies in this area. This paper gives reliability data for conformal coating users about the influence of thermal cycling.

This work sets out to characterise the protective properties of conformal coatings and how they degrade.

The approach dosed several commercial coatings with two different contaminants, a synthetic generic flux mixture of dibasic acids in both a solvent‐ and water‐based carrier, and sodium chloride. The protective properties were monitored using three complementary techniques: surface insulation resistance measurements, sequential electrochemical reduction analysis, and diffusion measurements.

The experimental approach was verified and the SIR measurements were shown to be the most valuable. Coatings offered varying levels of resistance to the contaminants, with the silicone coating being the most resistant. The flux variants generally proved more harmful to the coatings, suggesting that flux diffusion through the coating exceeded that of NaCl and hence led to greater electrochemical corrosion. Flux transmission through the coatings was verified by the diffusion measurements.

The project only investigated a limited number of contaminates on simple single sided boards. Future work will investigate coverage effects and a wider range of contaminants.

The work shows that coatings can allow diffusion of contaminates, particularly organics, which can lead to corrosion. The test methodology described here can be used to characterise coating susceptibility.

This work starts to develop for the first time a test methodology to characterise the protective properties of conformal coatings, and shows that flux, and hence other similar organic contaminants, may represent a protection challenge for some coating chemistries.

The purpose of this paper is to investigate the influence of composite coating structure on the reliability of adhesive flip chip joints. The need for conformal coating is considered, especially for medical applications, and medical sterilization is also considered.

Two test lots were assembled and one of them was sterilized using gamma sterilization. Both test lots were coated first with epoxy and then with Parylene C, resulting in a composite coating structure. The reliability was studied using a constant humidity test and the failure analysis was performed with cross‐sections and scanning electron microscopy analysis. These results were compared to earlier research results on conformal coatings.

The reliability of both test lots proved to be good. The composite coating structure shields the joints from humidity and improves the reliability compared to non‐coated test samples. When the conformal coating was compared to the pure Parylene C coated test lot, the reliability was almost the same. This leads to the conclusion that the epoxy layer in the composite coating structure has no value when long‐term reliability is considered. Gamma sterilization does not greatly affect reliability. The epoxy coating under the Parylene C layer cracked during reliability testing.

The paper shows the influence of composite coating structure on the reliability of adhesive flip chip joints, particularly important in medical applications.

Plastic ball grid array (PBGA) packages are non‐hermetic surface mount packages, designed in response to market demands for cost‐effective, high I/O count, small footprint, and low profile components. Because of the materials and construction, PBGA packages can be vulnerable to failure mechanisms associated with exposure to temperature and humidity. In some applications, conformal coating has been used as a potential means to mitigate these problems by enhancing moisture ingress resistance. This study focused on the ability of two popular kinds of conformal coatings to protect PBGA packages from moisture‐induced failures. As part of the study, PBGA packages with and without conformal coatings were subjected to moisture ingress, moisture desorption and unbiased high temperature high humidity tests. The principal failure mechanisms observed were delamination and cracking in the packages. Although it was observed that parylene coating did slow down the moisture ingress, the high temperature high humidity tests did not demonstrate that two tested conformal coatings had significant protection against moisture‐induced failures for PBGA packages.

This paper aims to presents a new method of investigation of local properties of conformal coatings utilized in microelectronics.

It is based on atomic force microscopy (AFM) technique supplemented with the ability of local electrical measurements, which apart from topography acquisition allows recording of local impedance spectra, impedance imaging and dc current mapping. Potentialities of the proposed AFM-assisted approach have been demonstrated on commercially available epoxy-coated electronic printed boards in as-received state and after six-year service.

The technique proved to be capable of identification, spatial localization and characterization of conformal coating defects.

The proposed approach can be utilized for assessment of protective film state in such demanding fields as electronics or electrotechnics where the classical techniques of anticorrosion coatings investigation cannot be employed due to small element dimensions and relatively low coating thickness.

The approach adopted by the author is novel in the field of organic coatings investigation.

Describes the use of a new type of UV cured coating and adhesive which are not adversely affected by fluorescing agents, so that increased quantities of fluorescing agents can be employed without retarding the depth of cure. Therefore, UV cured coatings and adhesives with this enhanced fluorescent response can readily be observed by the human eye using “black light” or by an on‐line electro‐optical device for quality control analysis of each electronic assembly.

There are many different types of protective coating available to the circuit manufacturer. Most are covered by United States Military Specification MIL‐I‐46058 and by British Standard Specification 5917 under such headings as acrylic, urethane, epoxide, silicone and paraxylylene. Whilst each of these coatings is effective for certain applications, all have limitations. Acrylics are easily applied but may have low resistance to abrasion and certain organic solvents. Urethanes may be applied only to very clean surfaces and usually have long cure times. Epoxides are strong with good abrasion resistance but exhibit high shrinkage and are very difficult to remove. Silicones have good electrical properties and temperature resistance but generally have poor adhesion to unprimed surfaces. Paraxylylene coatings have excellent abrasion resistance but are almost impossible to remove and expensive to apply (needing special equipment and the payment of royalties). This paper describes a new type of coating based upon fluoroacrylic polymers, developed in response to a US Mantech programme generated by Wright‐Patterson Air Force Base, which meets all the requirements of US MIL‐I‐46058 and is the only fluorocarbon coating included in the Qualified Products List for this specification.