Reliability of ACA bonded flip chip joints on LCP and PI substrates

Soldering &Amp; Surface Mount Technology

Heino

2010

Self Cite

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 2 40/þ 858C 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.

Section: Resultssupporting

confidence: 59%

“…Bonding conditions were chosen according to the ACF manufacturer's recommendations. The bonding pressure was selected from the wide range given by the ACF manufacturer according to earlier studies (Frisk and Ristolainen, 2005;Frisk and Cumini, 2006).…”

Section: The Bonding Processmentioning

confidence: 99%

Thermal cycling of flip chips on FR‐4 and PI substrates with parylene C coating

Kokko

Soldering &Amp; Surface Mount Technology

Heino

2010

Self Cite

“…After this the resistance of the samples was observed to increase at the low temperature extreme. Similar resistance variations and failure behaviour in earlier studies have indicated the development of adhesive cracking and interface delamination [9] [10]. That is, during the low temperature soak the materials of the assembly shrink causing adhesive cracks and delamination in the joints to open up.…”

Section: Resultsmentioning

confidence: 78%

Thermal cycling reliability analysis of an anisotropic conductive adhesive attached large-area chip with area array configuration

Kiilunen

Lahokallio

2015 IEEE 17th Electronics Packaging and Technology Conference (EPTC)

2015

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The reliability of adhesive flip chip attachments was studied. A large-area chip with a great number of contacts was attached onto a flexible polyimide substrate using anisotropic conductive adhesive film (ACF). The test samples were manufactured using various bonding forces and the reliability of the assemblies was examined using a thermal cycling test. Two temperature change rates were used in the cycling test to study the effect of the change rate on the observed failure times and modes. The results show that the ACF flip chip attachment of large-area chips with matrix array interconnections is an applicable technique. Furthermore, a significant increase in the reliability of the assemblies was obtained by increasing the bonding force. However, early failures were observed in all the samples, especially in the outermost adhesive interconnections. Failure analysis performed on the samples exhibiting early failures showed signs of adhesive delamination and silicon chip cracking. No clear differences in the results between the two temperature cycling tests used were observed. However, the faster temperature change rate seemed to cause a higher number of early failures.

“…There is also some difference between the LCP and the PI PCBs. When studied using cross sections, some over-etching of copper wires were seen in the PI substrates [9]. This decreased the contact area and may have lessened the reliability of the joints.…”

Section: Resultsmentioning

confidence: 98%

Liquid crystal polymer as a substrate material for flip chip ACA interconnections

3rd Electronics System Integration Technology Conference ESTC

Parviainen

Kokko

2010

Self Cite

In general higher packaging densities, thinner substrates and lighter products can be achieved using flexible printed circuit boards (FPCB) compared to traditional thicker fiber-reinforced printed circuit boards. Polyimide (PI) is popular substrate material in FPCBs due to its excellent properties. Liquid crystal polymers (LCP), on the other hand, are more rarely used in FPCBs. This is mostly due to their high cost and poor availability. However, they have an excellent combination of thermal, mechanical, chemical and electrical properties, which have caused increased interest to use them in several applications. In addition to thermoplastic PI and LCP materials, thin FR-4 laminates can be used as FPCB material. They have lower flexibility than PI and LCP, but also lower price and excellent availability. In this study the effect of substrate material to the reliability of flip chip interconnections assembled with anisotropically conductive adhesives (ACA) was investigated. Three different FPCBs made from PI, FR-4, and LCP were used. Several different tests were conducted. Results clearly showed that the reliability of ACA joints on LCP substrates was better compared to PI and FR-4 substrates under humid and corrosive environments.