A Novel Method for Embedding Semiconductor Dies within Textile Yarn to Create Electronic Textiles

Abstract

Electronic yarns (E-yarns) contain electronics fully incorporated into the yarn’s structure prior to textile or garment production. They consist of a conductive core made from a flexible, multi-strand copper wire onto which semiconductor dies or MEMS (microelectromechanical systems) are soldered. The device and solder joints are then encapsulated within a resin micro-pod, which is subsequently surrounded by a textile sheath, which also covers the copper wires. The encapsulation of semiconductor dies or MEMS devices within the resin polymer micro-pod is a critical component of the fabrication process, as the micro-pod protects the dies from mechanical and chemical stresses, and hermetically seals the device, which makes the E-yarn washable. The process of manufacturing E-yarns requires automation to increase production speeds and to ensure consistency of the micro-pod structure. The design and development of a semi-automated encapsulation unit used to fabricate the micro-pods is presented here. The micro-pods were made from a ultra-violet (UV) curable polymer resin. This work details the choice of machinery and methods to create a semi-automated encapsulation system in which incoming dies were detected then covered in resin micro-pods. The system detected incoming 0402 metric package dies with an accuracy of 87 to 98%.

Wash Testing of Electronic Yarn

“…To create the temperature sensing E-yarns, thermistors were first soldered onto the seven strand copper wire using solder paste (lead-free, antimony-free, rosin-based solder paste, part number 7024454: Nordson EFD, Dunstable, UK) and an infrared reflow soldering process (ATN LBS-G400; ATN, Berlin, Germany). The soldered thermistors, solder-joints and a supporting yarn (Vectran™) were subsequently encapsulated within an ultra-violet curable polymer resin micro-pod (diameter = 0.94 ±0.04 mm, length = 4.2 ± 0.49 mm) using an encapsulation system (as detailed elsewhere [14]). Three of cotton yarns (NM 30/1*2 Davidoff: Boyar Textile, Istanbul, Turkey) were then twisted around the copper wire populated with micro-pods using an Agteks DirecTwist 2B6 machine (Agteks, Istanbul, Turkey).…”

“…The entire circuit, with attached seven-strand copper wire (50 µm individual strand diameter; Knight Wire, Potters Bar, UK) and multifilament Vectran™ yarn, was encased within a tubular micro-pod with a diameter of 0.93 ± 0.04 mm and a length of 9.23 ± 0.49 mm, using the resin and procedure described above and elsewhere [14]. Three cotton yarns were twisted around the entire construction.…”

“…The E-yarns can contain any small-scale electronic component, such as a package die, to provide sensing or illuminating functions; a small flexible circuit; or a Micro-Electro-Mechanical Systems (MEMS) device. The electronic die or circuit is soldered onto a fine multi-strand copper wire (usually with a total diameter of around 130 µm) with each electronic component enveloped by a resin micro-pod [14]. Alternatively, dies can be soldered onto a circuit etched onto copper-coated polyimide film to enable advanced electronic circuits to be included within E-yarns [15]; the entire circuit can then be encapsulated with resin.…”

Flexible Sensors—From Materials to Applications

“…A more integrative approach looked into incorporating functional sensor strips as yarns in textile structures [388,[437][438][439]447]. Furthermore, Dias and coworkers [443,444,446,630,632,633] have pioneered a different method where surface mount sensor chips were seamlessly integrated within the core of a textile yarn and this yarn was used to fabricate textile garments. In general, the connections between the sensors and external circuits were made using conductive wires/threads [323,443,444,446,630,632,633], Bluetooth [555,634], NFC [635].…”

“…Furthermore, Dias and coworkers [443,444,446,630,632,633] have pioneered a different method where surface mount sensor chips were seamlessly integrated within the core of a textile yarn and this yarn was used to fabricate textile garments. In general, the connections between the sensors and external circuits were made using conductive wires/threads [323,443,444,446,630,632,633], Bluetooth [555,634], NFC [635]. The smart textile sensors were powered using lithium ion batteries [175], solar cells [175,187], flexible perovskite solar cells [636], triboelectric nanogenerators [404,637,638], pyroelectric nanogenerators [455], piezoelectric nanogenerators [637].…”