Semiconductor Encapsulation
Encapsulation (also called molding) protects packaged semiconductor dies from mechanical damage, moisture ingress, and environmental contaminants. After die attach and bonding, devices are encapsulated using epoxy mold compounds or sealed with lids (ceramic/metal) depending on performance, reliability, and hermeticity requirements. Proper encapsulation is critical for long-term reliability in consumer, automotive, industrial, and aerospace applications.
Process Overview
- Purpose: Provide mechanical protection, moisture barrier, and environmental sealing for the assembled die and interconnects.
- Sequence: Post-bond clean ? encapsulation (molding or lid attach) ? curing ? deflash/trim ? marking ? singulation (if panel/strip) ? final test.
- Scope: Plastic encapsulation dominates high-volume consumer and automotive; ceramic or metal lid sealing is used where hermeticity and high-temp operation are required.
- Interaction with Materials: Underfill (for flip-chip/microbump) typically precedes molding; choice of mold compound and lid adhesive must match CTE of die, substrate, and interconnects.
Encapsulation & Sealing Methods
| Method | Process | Advantages | Constraints | Typical Packages |
|---|---|---|---|---|
| Transfer Molding | Heated epoxy mold compound (EMC) is transferred under pressure into cavities around devices on a leadframe or substrate strip. | High throughput; mature; cost-effective for volume production. | Wire sweep risk; mold bleed/flash; tooling cost for new outlines. | QFN, QFP, SOP, many leadframe-based packages. |
| Compression Molding | Granular or sheet EMC compressed over components in an open mold, then cured. | Low wire sweep; good for thin packages, large dies, and 2.5D/3D modules. | Slower cycle time; tighter process control needed. | FO-WLP, SiP, fan-out packages, stacked die. |
| Glob-Top / Dam-and-Fill | Dispensed epoxy over die and wires; cured without a hard mold. | Low tooling cost; flexible for prototypes and small lots. | Lower dimensional control; limited mechanical robustness vs molded. | Sensors, modules, MEMS, low-volume custom packages. |
| Lid Attach (Non-Hermetic) | Metal or polymer composite lid bonded to substrate with adhesive or solder preform. | Better thermal path; shield options; protects delicate interconnects. | Not fully hermetic; adhesive outgassing must be controlled. | BGA, substrates in HPC/AI modules, RF modules. |
| Hermetic Sealing (Ceramic/Metal) | Kovar/ceramic packages sealed by solder, seam welding, or glass frit. | True hermeticity; high-temp and harsh-environment capable. | High cost; larger form factor; specialized supply chain. | Military/space, high-reliability sensors, optoelectronics. |
Representative Equipment Vendors
- Towa, Apic Yamada: Transfer and compression molding systems for EMC.
- ASMPT, Besi: Advanced packaging lines with molding, lid attach, and curing modules.
- Kulicke & Soffa: Encapsulation peripherals, plasma cleaners, and handling solutions.
- Palomar Technologies: Lid attach and seam sealing systems for hermetic and opto packages.
Materials & Consumables
- Epoxy Mold Compounds (EMC): Silica-filled epoxies with flame retardants and ion-scavengers to reduce corrosion and moisture uptake.
- Lids & Frames: Copper, aluminum, stainless, Kovar, or composite lids; ceramic frames for hermetic packages.
- Adhesives & Preforms: Epoxy adhesives, B-staged films, solder preforms, glass frit for hermetic seal.
- Coatings: Conformal coatings or parylene for added moisture protection (select applications).
Cleanroom & Environment
- Typically performed in Class 1000–10,000 assembly areas; moisture and ionic cleanliness are critical.
- MSL (Moisture Sensitivity Level): Packages are baked and dry-packed to JEDEC MSL ratings to prevent popcorning during board reflow.
- AMC (airborne molecular contamination) and outgassing control necessary for high-reliability and optical devices.
Reliability & Qualification
- Thermo-Mechanical: Temperature cycling, thermal shock, power cycling to assess CTE-mismatch stress.
- Moisture: MSL preconditioning, HAST (Highly Accelerated Stress Test), biased THB (Temperature Humidity Bias).
- Structural: Warpage, delamination (CSAM), voiding and adhesion audits post-mold.
Advantages & Constraints
- Advantages: Protects device and interconnects; scalable from low-cost plastic to hermetic packages; supports high I/O and high-power modules.
- Constraints: Wire sweep and mold bleed in transfer molding; CTE mismatch-induced stress; moisture-driven failures; higher cost/size for hermetic solutions.
Market Outlook
Encapsulation is evolving alongside advanced packaging. Compression molding and engineered EMCs are enabling thinner, larger-area packages for SiP, fan-out, and 2.5D/3D modules. For AI/HPC, lid attach with high-performance thermal interfaces is increasingly common. In automotive and industrial, enhanced moisture barriers and high-Tg materials are growing to meet AEC-Q100 and extended temperature ranges.