Semiconductor Manufacturing, Packaging and Materials Processes

Posted on Feb 16, 2026 in Technology

C6: Manufacturing & Packaging Processes

Organizational Overview of Semiconductor Manufacturing

IDM (Integrated Device Manufacturer): Handles the entire flow.
Fabless: Semiconductor design-centric operations.
Foundry: Wafer manufacturing-centric operations.
OSAT (Outsourced Semiconductor Assembly and Test): Specializes in packaging and testing semiconductors and wafers.

Basic Si Wafer Production Processes

Polycrystalline Silicon > Crystal Growth > Single Crystal Silicon Ingot > Crystal Trimming and Grinding > Slicing > Edge Rounding > Lapping > Etching (Chemical Polishing) > Polishing > Cleaning > Inspection > Packing / Shipping

Front End Process – Wafer Fab

Wafer Preparation > Semiconductor Circuit Design > Pattern Preparation > Oxidation Layering > Photoresist Coating > Stepper Exposure > Development > Etching > Ion Implantation > Chemical Vapor Deposition (CVD) > Metallization > Wafer Test

Back End Process (Assembly & Test)

Purpose of Semiconductor Packaging

Encase the chip in material (plastic or metal) to protect it from physical damage and corrosion, support electrical connection to the circuit board, and dissipate heat generated by the device.

BE1 – Wafer Back Grinding

Reduces the wafer thickness (typically 600 to 750 µm) down to the required thickness (50 µm to 75 µm) using an abrasive grinding wheel. This is usually done in two steps: coarse grind for bulk removal, then a finer grit polish for accurate thickness.

BE2 – Wafer Mounting

Mounts the wafer backside onto a sticky tape stretched onto a wafer frame to facilitate easy handling during the wafer saw and die-attach processes. The tape holds the wafer during dicing and die attaching.

BE3 – Wafer Dicing

Uses a die-sawing machine with a diamond saw blade to cut the wafer into individual die/pellets. De-ionized (D.I.) water is applied to the cut lines to prevent electrostatic issues or contamination.

BE3 – Die Attach (Die Bonding)

The die-attach machine picks up the only-good die and places it onto the leadframe using epoxy adhesive or solder. This involves epoxy dispensing, die pick-up (using a collet/ejector needle), and die placing.

BE4 – Die Attach Cure

Curing the die-attach paste to harden it and optimize its mechanical and electrical properties. Products are maintained at a temperature range, typically 125–175 °C, for a prolonged period.

BE5 – Wire Bonding

Establishes the electrical connection between the die and the leadframe, utilizing gold, copper, or aluminium wires. A good, metallized wire bond is achieved via a combination of temperature and ultrasonic energy.

BE6 – Moulding

The process of encapsulating the wire-bonded die by filling individual leadframe cavities with liquid resin (black plastic materials). This protects the device mechanically and environmentally from external factors such as light, heat, humidity, and dust.

BE7 – Post Mold Cure (PMC)

Accelerates the curing of the mold compound using rising temperature to ensure complete curing and improve the material’s physical properties.

BE8 – Lead Finish (Plating)

Applying a metal coat (e.g., Sn, SnPb, or Ni/Pd/Au, or Ag) over the package leads. This protects against corrosion and abrasion, improves solderability, and ensures mechanical/electrical connection to the Printed Circuit Board (PCB).

BE9 – Marking

Applies identification, traceability, and distinguishing marks to the package. Laser marking is preferred over ink for its higher throughput and better resolution.

BE10 – Trim / Form / Singulation

Trim: Cutting the dambars (which short the leads together). Form: Shaping the leads into the correct position. Singulation: Separating individual units from the leadframe strip and inspecting them (e.g., for lead coplanarity).

BE11 – Final Test (Electrical Testing)

Verifies the reliability of the package by electrifying it to test its function across various temperatures (ambient, hot, and cold). This process segregates functionally good devices from rejects into different bins.

BE12 – Final Visual Inspection (FVI)

Screens out visual defects on the finalized semiconductor package using magnification equipment (magnifier, microscope) or automatic inspection equipment. The goal is to ship only visually good parts to customers.

C7: Manufacturing & Packaging Materials

Levels of Integration

Level 1: Integration on Chip — Basic unit is the transistor (function cell); many are integrated to form a chip.
Level 2: Integration in Package — Basic unit is the bare chip/chiplet (function unit); units form a System-in-Package (SiP).
Level 3: Integration on PCB Board — Basic unit is the packaged chip or SiP (microSystem); these form larger systems.

IC Chip Package Types

Dual In Line Package (DIP), Small Outline Package (SOP), Quad Flat Package (QFP), Ball Grid Array (BGA), Chip Scale Package (CSP), Flip Chip Package (FCP)

Key Chip Components and Materials

Die, die passivation, conformal coating.

1st Interconnect: Wire, bumps, tape.

Leadframe (Cu, Alloy 42).

Solder (Die attach types: metallic, polymeric, glassy, anisotropic).

Cases and Encapsulants (moulding compounds, glob top, underfill resins, ceramic cases). Heat sink materials (substrates like BT, FR4, Al2O3, AlN, PTFE).

2nd Interconnect: leadframes, solder balls, pin.

Printed Circuit Board

Die Semiconductor Materials

A semiconductor is defined as a material with electrical conductivity between that of a conductor and an insulator, generally ranging from 10³ to 10^-8 S/cm. Common materials include Silicon (Si), Germanium (Ge), GaAs, InP, and GaN, with silicon being the most widely used as a substrate for complex Very Large Scale Integration (VLSI) ICs and simple devices like diodes and transistors. Silicon production, often utilizing the Czochralski (CZ/MCZ) Process, involves the purification of sand into polysilicon using trichlorosilane and hydrogen, followed by melting the polysilicon at over 1400 °C and slowly pulling a rotating single-crystal “seed” up from the melt to form a large single-crystal ingot. Finally, a conformal coating is applied, which functions as a primary passivation layer to provide mechanical and environmental protection to the die and PCB against moisture and corrosive agents; this coating is most commonly made from materials like polyurethanes, silicones, epoxies, or high-performance polyimides.

Lead Frame

The leadframe serves several crucial functions, including acting as a holding fixture during molding, indexing tool-transfer mechanisms, creating a dam to prevent plastic overflow between leads, providing a chip attach substrate and support matrix for the plastic, and functioning as both an electrical and thermal conductor from the chip to the board. Material criteria for leadframes demand high electrical and thermal conductivity (to dissipate heat), a coefficient of thermal expansion (CTE) comparable to the IC, good adhesion to die-bonding adhesive, high yield strength/ductility, and resistance to oxidation/corrosion at high temperatures.

Typical materials include copper alloys (C-194 & C-195), which offer a low thermal mismatch (CTE = 17–18 ppm/°C) with encapsulating moulding compound (EMC), and high thermal and electrical conductivity, making them suitable for devices dissipating much heat; another material is Alloy 42 (42Ni-58Fe), which provides a very low thermal mismatch (CTE = 4.0–4.7 ppm/°C) with Si die (CTE = 2.3–2.6 ppm/°C), high yield strength, and good formability, though its thermal and electrical conductivity are poor, making it better for memory devices producing little heat. Finally, plating is necessary to prevent oxidation of the base metal, which would insulate the electrical connection, and plating materials must ensure good wire bondability (e.g., spot Ag), lead conductivity/platability, and solderability (e.g., eutectic solder 63%Sn-37%Pb); a two-layer plating is common, utilizing nickel (Ni) electrolytic coating as an undercoat for better adhesion, followed by a primary lead finish such as Au, Pd, Ag spot plating, or solder plating.

Die Attach

Die attach is the process of mechanically bonding the die to the leadframe, serving to provide heat transfer and sometimes electrical contact with the die backside. The materials used must meet stringent criteria, requiring high shear bond strength, high thermal conductivity (often achieved using Al2O3, B2O3, or BN as fillers), electrical conductivity (typically achieved with Ag or Ni fillers), and minimal void content or impurities.

Die attach materials are broadly categorized as organic or inorganic. Organic die attach includes epoxies (thermoset), which have the widest commercial use (approximately 80% market share) and can be filled with up to 80% silver for enhanced electrical and thermal conductivity, or Al2O3 for electrical isolation; and polyimides (thermoplastic), which are advantageous in high-temperature applications (Tg ranging from 180 to 275 °C) and offer the possibility of rework. Inorganic die attach methods include silver-filled glasses, which use glass adhesion (lead borate) in a paste applied to the die backside, with silver included to enhance thermal conductivity; and solder die attach, which utilizes solder paste or preform, with typical solders including 80Au/20Sn, although a common issue is high die stresses caused by thermal mismatch and a high solidification temperature (365 °C).

Solder Materials and Lead-Free Transition

Solder is defined as a coalescing metal filler used for welding that provides electrical, thermal, and mechanical linkages, wetting the surfaces via capillary action and characterized by a liquidus temperature of C or lower. Solder alloys historically relied on Sn/Pb but may include Ag, Bi, In, Sb, or Cd. Solder paste is formulated as a homogeneous mixture composed primarily of solder powder/flakes (88–94 wt%), along with fluxes (5–10 wt%) to clean substrate metal oxides, and a vehicle (1–3 wt%) containing solvents and thixotropic agents to prevent settling.

Flux types, which ensure surfaces are “scientifically” clean for good solderability, include rosin-based, water-soluble (often preferred for performance), and no-clean varieties (which require a nitrogen protective atmosphere). The significant industry shift towards lead-free replacement was driven by legislation such as the EU’s RoHS directive, which prohibited significant quantities of lead in most consumer electronics starting in July 2006, recognizing that lead poisoning causes severe neurological and gastrointestinal problems. Crucially, lead-free replacements must satisfy stringent requirements, including having a melting (or solidus) temperature similar to solder, possessing comparable or better physical properties (such as ductility, tensile strength, and electrical conductivity), demonstrating low toxicity, and maintaining compatibility with existing flux and metallisation systems.

Wire Bonding Materials

Wirebonding is a dominant interconnection technology whose function is to connect the device bond pad to the lead wire or to another device bond pad. The selection criteria for wire materials include low electrical resistivity, high shear and tensile strength, a suitable CTE, and a low risk of forming excessive intermetallics.

Gold (Au) wire is highly valued for its excellent thermal and electrical conductivity, chemical stability (non-oxidizing), and ease of process control, although it is very expensive, possesses low mechanical strength, and exhibits poor electromigration resistance, often requiring additives like Be or Cu to enhance strength. In contrast, copper (Cu) wire offers superior electrical and thermal conductivity to gold, low cost, and resistance to creep, but it oxidizes easily, demanding a protective gas ambient, and its hardness necessitates higher bonding forces, making process control more demanding. Silver (Ag) wire boasts the best electrical and thermal conductivity among the metals and excellent reflectivity, yet it is stiffer than gold, is highly prone to sulfur corrosion (tarnishing), and experiences adhesion issues under humidity. Lastly, aluminum (Al) wire is cost-effective, low in density, and offers high-temperature stability due to its stable oxide layer, but it has lower conductivity than Cu or Au and is typically restricted to the low-temperature wedge-wedge bonding process.

Cases and Encapsulants

Cases and encapsulants are essential for mounting devices and interconnections, acting as a crucial path for dissipating heat, and most importantly, providing protection to the package contents from environmental contaminants and operational stresses. These packages are broadly classified as cavity versus noncavity types, and as hermetic (utilizing ceramic or metallic cases for high-reliability military/government applications) versus non-hermetic (plastic cases).

Plastic Encapsulated Microelectronics (PEMs) dominate the industry, accounting for over of the market due to their low cost, light weight, suitability for mass production, and satisfactory reliability. Among plastic encapsulants, epoxies are the most widely used, noted for their low initial viscosity, high elastic modulus, good chemical resistance, and strong bonds with the die and leadframe. Silicones offer high heat resistance (up to C) and ductility, making them suitable for automotive vibration damping, although they have drawbacks like high CTE and a tendency toward delamination due to poor adhesion. Conversely, hermetic cases, which use ceramics like or AlN, or metal alloys like Kovar, provide superior stability and excellent moisture/gas sealing for a longer lifespan, but they are significantly high cost, heavier, and complicate thermal expansion matching.

Heat Sink Materials and Thermal Interface Materials (TIMs)

The primary role of a heat sink is to conduct and radiate the heat generated by device operations, particularly in power applications, requiring materials characterized by high thermal conductivity, low CTE, and low density. While traditional copper is thermally conductive, it suffers from high density and a high CTE (), and aluminum provides low density but lower conductivity and an even higher CTE (); specialized materials like expensive carbon-carbon composites offer superior performance, boasting very high thermal conductivity (W/mK) and a low CTE.

To maximize heat flow across interfaces, thermal interface materials (TIMs) are inserted between components (like the device and the heat sink) to reduce thermal resistance and minimize stress arising from CTE mismatch; TIMs must be highly thermally conductive, deformable (low viscosity), non-toxic, and maintain long-term reliability. TIMs are available in various forms, including pads, gap fillers (which cure to conform to geometries), phase change materials (PCMs), and grease (which fills voids well). The heat transfer properties of TIMs are primarily governed by high-conductivity fillers, such as ceramic types like boron nitride (300 W/mK) and aluminum nitride (220 W/mK), or advanced carbon fillers like carbon fiber (800 W/mK) and, most notably, carbon nanotubes (CNTs), which exhibit extremely high thermal conductivity (3,000 W/mK) and can significantly improve the thermal performance of composites.

Printed Circuit Boards (PCBs)

A printed circuit board (PCB) is fundamentally a conductive circuit pattern created on or within a dielectric base material, requiring material selection criteria that emphasize high insulation resistance, high wiring capability, low CTE, high thermal conductivity, high resistance to soldering temperatures (), and dimensional stability.

Organic PCB types include rigid boards (copper patterns on a composite laminate), flexible boards (which utilize flexible base films like polyimide/Kapton or PTFE and are essential for continuous movement applications), rigid-flexible boards (combining flexible layers with rigid caps), and moulded boards (where conductors are applied to extruded or injection-moulded thermoplastic resin). Rigid PCBs are structurally categorized as single-sided, double-sided (with interconnection via plated vias), or as a multi-layered board (MLB), which is fabricated by laminating three or more pre-etched conductive layers.

Flexible PCBs specifically rely on ductile copper foil as the conductor, base dielectric films like polyimide or polyester, and adhesives such as acrylics (favoured for high-temperature soldering), epoxies, or polyesters.