EMC (Epoxy Molding Compound)

Notes

Dominated by a handful of Japanese and Korean suppliers, making it a quiet single-source risk in the packaging supply chain.

Overview

In chip packaging, EMC (epoxy moulding compound) is the filled thermosetting resin that is moulded around dies and their wires to form the solid body of most plastic chip packages. It protects the die from moisture, contamination and mechanical damage, and its properties, especially how much it expands with heat, strongly affect package warpage and reliability. It is mostly silica filler held in an epoxy resin.

How it works

A moulding compound is a blend of epoxy resin, a hardener, a high proportion of fine silica filler, and smaller amounts of catalysts, flame retardants, coupling agents, release agents and pigments. The filler lowers the coefficient of thermal expansion towards that of silicon and copper, raises thermal conductivity and reduces moisture uptake. Suppliers formulate different grades for different packages, varying filler size and loading, flow, glass transition temperature, stiffness and adhesion.

In transfer moulding, the most common method, solid pellets of compound are heated until they flow, then pushed under pressure through channels into cavities around the parts on a lead frame or substrate strip, where they cure into a hard thermoset. Compression moulding, which spreads compound over a whole strip or wafer and presses it into shape, is used for thin packages, large panels and wafer-level and fan-out packaging, where flowing compound could sweep fine wires or move dies. After moulding, parts are post-cured to complete the reaction.

Getting the compound right is a reliability task. Mismatched expansion causes warpage and stress that can crack dies or lift bonds during temperature cycling; absorbed moisture can turn to steam during solder reflow and crack the package, which is why parts are classified for moisture sensitivity under the joint IPC and JEDEC J-STD-020 standard.

Examples

• A low-stress, high-filler compound chosen for a large BGA to limit warpage during reflow.
• Transfer moulding of QFN packages on a lead frame strip, followed by post-cure and singulation.
• Compression moulding used for a fan-out wafer-level package to avoid moving the embedded dies.
• A package cracking during reflow traced to absorbed moisture, prompting a stricter moisture sensitivity level.
• A change of compound supplier handled as a product change with new qualification data.

Why it matters

Package materials engineers, moulding process engineers, reliability and package warpage engineers choose and qualify moulding compounds, and a change of compound is a significant product change that customers may need to be told about. In advanced packages the compound also affects how far dies shift during moulding, which matters for fine-pitch wiring.

Related terms

• MUF
• Warpage
• CTE
• Delamination
• EMI
• CISPR 25

Where it appears on the Hub

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