ASP‑23 Powder Metallurgy High‑Speed Steel – Why Is It Increasingly Used in Chip Encapsulation Molds?

In the semiconductor encapsulation field, the selection of mold materials directly affects encapsulation quality, mold life, and production efficiency. In recent years, ASP‑23 (also known as ASP23) powder metallurgy high‑speed steel has been increasingly widely used in IC encapsulation molds, lead frame molds, and similar applications. What exactly is this material? Why is it suitable for encapsulation molds? And what should be noted during machining?

What Kind of Material Is ASP‑23?

ASP‑23 is a powder metallurgy high‑speed steel from ASSAB (Sweden), belonging to the chromium‑molybdenum‑tungsten‑vanadium powder high‑speed steel family. Unlike traditional ingot‑cast high‑speed steel, it is manufactured using a powder metallurgy process – molten steel is first atomized into fine powder and then formed by hot isostatic pressing. The direct result of this process is: extremely uniform carbide distribution, fine grain size (1–3 μm), and complete elimination of the large carbide segregation common in traditional processes.

Typical chemical composition of ASP‑23 includes: carbon 1.28%, chromium 4.2%, tungsten 6.4%, molybdenum 5.0%, vanadium 3.1%. Delivery hardness is approximately 260HB, and hardness after heat treatment can reach HRC64‑66.

What Role Does ASP‑23 Play in Chip Encapsulation Molds?

ASP‑23 is mainly used in semiconductor IC encapsulation molds (such as encapsulation molds, cavity strips, etc.). In the chip encapsulation process, ASP‑23 material is heat‑treated and then used to manufacture molds. Through the transfer molding process, environmentally friendly plastic materials (EMC) are encapsulated and formed, and finally mounted onto the lead frame to complete chip encapsulation.

ASP‑23 is chosen as an encapsulation mold material primarily for the following reasons:

Uniform carbide distribution and good machining consistency. The powder metallurgy process makes carbide distribution extremely uniform, ensuring uniform erosion during EDM without localized over‑erosion or defects. This is especially important for encapsulation molds with many cavities and high consistency requirements.

Good dimensional stability during heat treatment. ASP‑23 exhibits small and predictable dimensional changes during heat treatment, meaning mold deformation after hardening is controllable and machining allowances can be precisely reserved.

Balance of high hardness and toughness. Hardness after heat treatment can reach HRC64‑66 while maintaining good toughness, suitable for withstanding repeated loads during encapsulation.

Suitable for PVD coating. The uniform carbide distribution of ASP‑23 improves coating adhesion, and PVD coating can further enhance mold surface performance and life.

Why Is EDM Indispensable for ASP‑23 Mold Machining?

ASP‑23 has extremely high hardness after heat treatment, making traditional cutting very difficult. EDM, Brass Wire Cut EDM, or laser cutting are typically used. In actual encapsulation mold manufacturing processes, the EDM machine (Die‑sinker EDM Machine) undertakes the critical task of cavity finishing.

The advantages of EDM in machining ASP‑23 include:

Not limited by material hardness. Regardless of whether ASP‑23 is heat‑treated to HRC62‑64 or higher, EDM removes material through discharge without relying on tool cutting – material hardness does not affect machining feasibility.

Capable of machining complex cavity structures. Encapsulation mold cavities often have complex geometries and micro‑features. The Die‑sinker EDM Machine can “copy“ complex cavity structures through formed electrodes. The AF Series achieves stable machining in general mold applications such as narrow slot machining.

Ensuring multi‑cavity machining consistency. Multi‑cavity encapsulation molds have extremely high requirements for dimensional consistency across each cavity. The AF Series is equipped with an intelligent discharge control system that precisely detects and controls each discharge pulse, while the AC servo full closed‑loop motion control system performs real‑time detection, feedback, and correction of each motion axis position.

Achieving excellent surface quality. The AF Series achieves optimal surface roughness that meets the strict requirements of encapsulation molds for cavity surface quality.

What Precautions Should Be Taken for ASP‑23 EDM?

During EDM of ASP‑23, a “white layer“ (recast layer and re‑hardened untempered layer) forms on the surface. Both structures are relatively brittle. To improve mold performance, it is recommended to use “fine discharge“ after machining – low current, high frequency. After EDM, grinding or polishing should be performed to remove the surface white layer, followed by tempering again at around 535°C. Alternatively, low‑temperature tempering at 300‑400°C can eliminate approximately 70% of machining stress, avoiding micro‑cracks in subsequent use.

What Can the NOVICK AF Series Offer for ASP‑23 Encapsulation Mold Machining?

To address the precision cavity machining requirements of high‑hardness mold materials such as ASP‑23, the NOVICK AF Series precision CNC Die‑sinker EDM Machines offer the following features:

High‑rigidity Ram‑type structure. The fixed worktable ensures that workpiece weight does not affect motion axis accuracy. The AF70 can handle maximum workpiece weights up to 2000kg.

AC servo full closed‑loop motion control. Real‑time detection, feedback, and correction of each motion axis position ensures long‑term machining stability.

Intelligent discharge control system. Automatically matches machining strategies for different stages, balancing machining efficiency and surface quality.

Mirror‑grade surface quality. Optimal surface roughness reaches Ra < 0.1μm, meeting the surface requirements of encapsulation mold cavities.

Flexible configuration. Supports optional C‑axis rotary machining, linear scale feedback system, automatic tool changer, automation interfaces, and more.

Summary

ASP‑23 powder metallurgy high‑speed steel, with its uniform carbide distribution, excellent heat treatment dimensional stability, and good balance of high hardness and toughness, is increasingly used in semiconductor encapsulation applications such as IC encapsulation molds and lead frame molds. The high hardness of ASP‑23 after heat treatment makes die‑sinking EDM a key process for cavity finishing.

The NOVICK AF Series precision CNC Die‑sinker EDM Machines deliver corresponding performance in high‑rigidity structure, positioning accuracy, mirror‑finish machining, and machining stability – providing reliable technical solutions for precision cavity machining of ASP‑23 encapsulation molds.