Microsystems Development and Packaging Luiz Otvio Saraiva Ferreira

Microsystems Development and Packaging Luiz Otávio Saraiva Ferreira LNLS lotavio@lnls. br

OUTLINE • • • Materials and Manufacturing Process Choosing Substrate Modelling CAD Software Packaging

Basic Steps • Good knowledge of system requirements. • Interview with potential users. • Understanding of the application environment. • GOOD VISION OF THE MARKET.

Choosing Materials and Manufacturing Process • MATERIALS PROCESS

Choosing the substrate • How must be the format of the packaging, and how the packagint interfaces to the real world? – The package and its interfaces define the cost and size of the product, the nature of the device that goes inside it, and the answer to many of the questions presented bellow. • Is it needed to integrate electronic functions on the substrate? – If yes, a high impedance substrate must be chosen.

Production Scale • How many devices will be produced (production volume or number of units) and what is its complexity (number of devices per sample)? – This number may suggest serial production (small quantities), hybrid production (wide quantities), or batch production (very wide quantities). – High complexity may suggest batch production.

Cost • What is the unity cost? – High ( > US$40. 00) serial prod. – Low (< US$2. 00) batch prod. – Very low (glicose sensor, US$0. 20) continuous production process. • The substrate is only a support: glass, ceramic, plastic or paper. • The substrate has mechanical function: silicon is na excelent candidate. • The substrate has optical function: Ga. As and PMMA.

Modularity • Is modularity needed? – It is importan on chemical sensors arrays. • The integration is undesirable because the incompatability between the deposition process of different sensors on the array. • What are the lateral tolerances and the aspect ratio of the devices? – It is not yet possible to have very small lateral tolerances. • 100µm wide lines (optic lithography) 1% is good. – Aspect ratio more than 20: 1 • Wet anisotropic etch of Si. • Anisotropic plasma etch (DRIE). • LIGA Technology (UV or X).

Environment • To what is the environment the system will be exposed (air, water or other)? – Sensors exposed to aquous environments like blood have more packaging problems, and are more dificult to integrate with electronics. • Which substrate makes the packaging requirements less stringent? – Sensor in aqueous solution • ceramic substrate requires no protection of the sides. • silicon is difficult to insulate and package, because the conductive medium might short out the sensor signal via the Si sidewalls. . • 2 D or 3 D parts? – 3 D conventional precision engineering. • Diamond turning. . • Molding. – 2 D lithographic process.

Thermal • Thermal requirements? – Maximum temperature. • Si electronic circuits: T < 150 o. C. • T > 150 o. C SOI, Ga. As. – Thermal conductivity? – Is thermal matching with other material important? • Flatness requirements (often in connection with the optical properties of the substrate)? – Average roughness, Ra? – One or both sides polished? • Optical requirements? – Transparency in certain wavelength regions? – Index of refraction? – Reflectivity?

Electromagnetics • Electrical and magnetic requirements? – Conductor X Insulator? – Dielectric Constant? – Magnetic properties? • Process compatibility? – – Is the substrate part of the process? Chemical compatibility? Ease of metallization? Machinability? • Strain-dependent properties? – – Piezoresistivity? Piezoelectricity? Fracture behavior? Young´s modulus?

Most used substrates • • Silício. Quartzo. Vidro. Alumina. Plastic. Aluminum. Poli-Si, Zn. O, Ni. Ti, PVDF, Si. C.

Formulation and Use of Macromodels • Lumped mechanical equivalents for complex structures. • Equivalent electric circuit of a sensor. • Feedback representation for coupled-force problems.

Micromechanical Device Mathematic Formulation Equivalent Electromechanical Diagram

Analog Hardware Description Language HDL-A , Spectre-HDL , VHDL 1076. 1 , VHDL-AMS LIBRARY conserved_systems; USE conserved_systems. nature_pkg. ALL; ENTITY piezopress_equ IS GENERIC (h: real : = 17 e-6; -- plate thickness a: real : = 1 e-3; -- plate side length r 0: real; -- nominal resistance rs: real); -- sensitivity PORT (TERMINAL fp: fluid; -- fluidic pin TERMINAL ep: electrical); -- electrical pin END ENTITY piezopress_equ; ARQUITECTURE equ OF piezopress_que IS CONSTANT e 0: real : = 146. 9 e 9; -- Si elasticity [N/m**2] CONSTANT v 0: real : = 0. 1846; -- Si Poisson’s ratio CONSTANT df: real : = e 0*h**3/(12*(1 -sqr(v 0)); -- rigidity QUANTITY v ACROSS i THROUGH ep TO ground; QUANTITY p ACROSS ft TO fld_gnd; QUANTITY w 11: real; -- deflection coefficient BEGIN (w 11/h)**3 + 0. 2522*w 11/h == 0. 000133*p*a**4/(df*h); i == v/(r 0 + rs*2. 5223*1. 5895 e 9*w 11); END ARQUITECTURE equ; Piezo-resistive pressure sensor

Basic Simulation Tools • Analysis Basic Phenomena Thermal Heat flow Mechanical and structural Deformation Electrostatic Capac /charge dens Magnetostatic Induct / flux dens Fluid Pressure and flow

CAD Software for Microsystems Coventor, Inc Coventor. Ware software http: //www. coventor. com

Conceptual Design and Simulation 1 2 3 4 Coyote Systems http: //www. coyotesystems. com

Materials Database Intelli. Suite™ (Intelli. Sense) Corp. (http: //www. intellisense. com)

Process Simulators Intermediate steps in the fabrication of a thermal actuator from the University of California, Berkeley, developed using the MUMPs process. Simulator of anisotropic etch of silicon. Intelli. Suite™ (Intelli. Sense) Corp. (http: //www. intellisense. com) Foundry-ready process templates include: • Cronos – MUMPs® • Sandia – SUMMi. T • Standard MEMS – polysilicon process • AMI – MOSIS® • LIGA • SCREAM

Device Analysis • Linear and non-linear analysis • Static, steady state, and transient analysis • Fully 3 D coupled dynamics analysis • Parametric variation of parameters • Takes into account fabrication processinduced effects • Submodeling, symmetry, and other size reducing techniques • Animation and color mapping of results Intelli. Suite™ (Intelli. Sense) Corp. (http: //www. intellisense. com)

Packaging • More than 70% of the microsystem cost. • Much more complex than ICs. – Must protect from and enable interaction with the environment. – Communication channels. – Remove heat. – Handling and tests. – Chemical protection. – Adequate interior (vacuum).

Packaging Levels – 0) Elementary component of a device. – 1) Device. Sensor or IC. – 2) Packaged device or hybrid module. – 3) Printed Circuit Board. – 4) Box or chassis. – 5) Complete System.

Adhesion • Direct adhesion: Si-Si, Polymer. Polyímer. • Anodic bonding: Si-Glass. • Si plus 1 to 2µm PSG 30’ @ 1100 o. C • Eutetic bond: Si-Au/Si @ 363 o. C. • Photoresist: AZ 4000, SU-8, Polyimide, PMMA, PDMS, etc.