Kirsi Saarinen and Pekka Heino
Personal and portable electronic devices are becoming an important part of the everyday lives. Electronics miniaturization has been and continues to be the most important driver…
Abstract
Purpose
Personal and portable electronic devices are becoming an important part of the everyday lives. Electronics miniaturization has been and continues to be the most important driver in this development. The current level of miniaturization has made the use of solder joints challenging and new methods, such as adhesive attachments, have been developed. The applicability of these methods depends crucially on their long‐term reliability. Typical failures mechanisms in adhesive connection include cracking, open joints and delamination. Moisture is the principal cause of failures in adhesive attachments. The purpose of this paper is to examine the long‐term effects of moisture and extended temperature on non‐conductive adhesive (NCA) attachments.
Design/methodology/approach
Moisture and extended temperature on NCA attachments are examined by strength tests and by finite element models.
Findings
The increase in temperature and moisture induces stresses on the interface of the adhesive and the chip. In the experiments, it is found that the adhesion strength of the adhesive decreased as a function of the time for which the samples are in a humid environment. Failures due to delamination are seen to be the result of these two mechanisms.
Originality/value
Reduction of pitch causes manufacturing problems in direct solder attachments. This paper examines a promising technique to overcome this problem by using adhesive attachment. Instead of solder joints in flip chip attachment, the chips can be attached to the substrate, or components can be attached to a printed wiring board, with adhesives.
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Kati Kokko, Hanna Harjunpää, Pekka Heino and Minna Kellomäki
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
The paper shows the influence of composite coating structure on the reliability of adhesive flip chip joints, particularly important in medical applications.
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Henna Heinilä, Jarno Riistama, Pekka Heino and Jukka Lekkala
The purpose of this paper is to present the stages for manufacturing a low‐cost miniaturized prototype device, which observes the restrictions of implantable medical devices. The…
Abstract
Purpose
The purpose of this paper is to present the stages for manufacturing a low‐cost miniaturized prototype device, which observes the restrictions of implantable medical devices. The device measures the electrocardiography. The power for the implant is received passively as the same magnetic field as data is transferred to the reader device.
Design/methodology/approach
In this manufacturing technique, only easily attachable commercial available components are used, etching is used to simply produce a low‐cost double‐sided flexible printed circuit board which is converted to 3D by folding.
Findings
The circuit board was folded into the final shape after component attachment and the final result was a compact 3D package within the specifications determined by the electronics designer. The miniaturized prototype device was successfully tested both in vitro and in vivo.
Originality/value
The manufacturing technique of the sensing device can be readily adapted to other devices that need to be miniaturized. The coatings used for electrical insulation and chemical protection and the type of adhesives used for folded packages are easily utilized in similar miniaturization prototypes. By using bare chips, the final product would have been even smaller but for prototyping it is cheaper and faster to use easily acquired and attached components. In the case of mass production, the whole new design, where bare chips with flip chip attachments, integrated passives and/or stacked 3D packages with design considerations such as electrical, thermal and mechanical engineering is justified.
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Kati Kokko, Laura Frisk and Pekka Heino
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
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Kati Kokko, Hanna Harjunpää, Anna‐Maija Haltia, Pekka Heino and Minna Kellomäki
The purpose of this paper is to study epoxy and parylene C‐coated samples. These coatings are used to protect the electronic devices from harsh environments. The effect of these…
Abstract
Purpose
The purpose of this paper is to study epoxy and parylene C‐coated samples. These coatings are used to protect the electronic devices from harsh environments. The effect of these conformal coatings on electronics reliability is considered.
Design/methodology/approach
Epoxy coating is applied using dip coating and parylene C is applied with the vapour deposition polymerisation method. Test chip used is joined using flip‐chip technology and an anisotropically conductive adhesive. Reliability of the test samples is evaluated in a constant humidity test, where test conditions are 85°C and 85%RH. The test lasts 4,000 h. Failure analysis is carried out by cross‐sectioning failed samples and using scanning electron microscopy for closer analysis.
Findings
The results show variation in the reliability of adhesive joints with different conformal coating materials. Failure analysis highlights explicit failure mechanisms. Adhesion testing is also carried out on the test samples after constant humidity testing. The results of these reliability tests indicate clearly that parylene C is a more reliable choice of conformal coating than epoxy.
Originality/value
The paper shows the influence of certain conformal coatings on the reliability of adhesive flip‐chip joints. In medical applications, reliability plays an important role.
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Atte Oksanen, James Hawdon, Emma Holkeri, Matti Näsi and Pekka Räsänen
The prevalence of online hate material is a public concern, but few studies have analyzed the extent to which young people are exposed to such material. This study investigated…
Abstract
Purpose
The prevalence of online hate material is a public concern, but few studies have analyzed the extent to which young people are exposed to such material. This study investigated the extent of exposure to and victimization by online hate material among young social media users.
Design/methodology/approach
The study analyzed data collected from a sample of Finnish Facebook users (n = 723) between the ages of 15 and 18. Analytic strategies were based on descriptive statistics and logistic regression models.
Findings
A majority (67%) of respondents had been exposed to hate material online, with 21% having also fallen victim to such material. The online hate material primarily focused on sexual orientation, physical appearance, and ethnicity and was most widespread on Facebook and YouTube. Exposure to hate material was associated with high online activity, poor attachment to family, and physical offline victimization. Victims of the hate material engaged in high levels of online activity. Their attachment to family was weaker, and they were more likely to be unhappy. Online victimization was also associated with the physical offline victimization.
Social implications
While the online world has opened up countless opportunities to expand our experiences and social networks, it has also created new risks and threats. Psychosocial problems that young people confront offline overlap with their negative online experiences. When considering the risks of Internet usage, attention should be paid to the problems young people may encounter offline.
Originality
This study expands our knowledge about exposure to online hate material among users of the most popular social networking sites. It is the first study to take an in-depth look at the hate materials young people encounter online in terms of the sites where the material was located, how users found the site, the target of the hate material, and how disturbing users considered the material to be.