Abstract
Die-level thinning, handling, and integration of singulated dies from multi-project wafers (MPW) are often used in research, early-stage development, and prototyping of flexible devices. There is a high demand for thin silicon devices for several applications, such as flexible electronics. To address this demand, we study a novel post-processing method on two silicon devices, an electrochemical impedance sensor, and Complementary Metal Oxide Semiconductor (CMOS) die. Both are drawn from an MPW batch, thinned at die-level after dicing and singulation down to 60 µm. The thinned dies were flip-chip bonded to flexible substrates and hermetically sealed by two techniques: thermosonic bonding of Au stud bumps and anisotropic conductive paste (ACP) bonding. The performance of the thinned dies was assessed via functional tests and compared to the original dies. Furthermore, the long-term reliability of the flip-chip bonded thinned sensors was demonstrated to be higher than the conventional wire-bonded sensors.
Highlights
If the transducer can be integrated in the close vicinity of a Complementary Metal Oxide Semiconductor (CMOS) chip (e.g., system in package (SiP) configuration), the device becomes ideal for several applications, such as patch sensors and large-area electronics
The thermosonic flip-chip process has the advantage of low bonding force, low temperature, and short bonding time yielding a strong metallurgical joint [18,19]. This process is a clean, lead-free, and dry process which is well suited for hybrid integration of electronic packages [20]
The ~3 mm × 3 mm CMOS chips with an initial thickness of 790 μm were fabricated in a commercial foundry and diced from a 12-inch multi-project wafers (MPW)
Summary
Flexible and conformal systems are one of the major research areas in today’s electronics industry. If a sensor and its associated silicon-based readout electronics become flexible, the utility of the device goes far beyond the traditional applications based on rigid printed circuit boards [1–3]. If the transducer can be integrated in the close vicinity of a CMOS chip (e.g., system in package (SiP) configuration), the device becomes ideal for several applications, such as patch sensors and large-area electronics. If it is an electrochemical sensor system exposed to a harsh environment (e.g., medical implants, water/fluid sensors), hybrid bonding, encapsulation, and packaging become critical. Copaotsiendg taondcounsvinengtpiohnoatlosmpainsk-cso[a5t]i.nTghainnndinugsionfgspinhgoletocmhiapsskiss[a5l]s.oTchhinalnleingionfgsaingdlerecqhuiiprsesis maolsdoifichcatliloengsitnogsatannddraerqduwireasfemr othdiinfinciantigo.nHs toowsetvanerd,airndawn aMfePrWth,insonmineg.dHevoiwceesvreerq, uiniraen thMinPnWin,gsowmheildeeovtihcesrsredqouniroetth[1i2n]n.inTghewwhialefeorthisefirsrsdtodnicoetd[1a2n].dThtheewn atfheer ins dfiirvsitdduicaelddaiensd atrheetnhitnhneeidn.dCivoirdruesapl odniedsinagrley,thinintnheisd.stCuodryr,easpdoien-dleinvegllyth, iinnntihnigs srotuudtey,foardMieP-lWeveclhtiphsinwniansg sorouugthetfaosr tMhePWonlcyhivpiasbwleasopsotiuognhttoatshtihneCoMnlOy Sviaanbdlesoepntsioorncthoitphsi.n CMOS and sensor chips
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