Introduction

In patentability searching, patent classification tools help address an unavoidable blind spot in keyword searching: different patents may describe the same technology using entirely different terminology. If your search strategy relies solely on keywords, the risk of missing relevant prior art always exists. Patent classification tools were designed precisely to solve this problem — they provide structured indexing of patents based on the technical solution itself rather than the language used to describe it.

But the question is: IPC, CPC, FI/F-Term… what are the distinguishing features of each tool? How do you find the correct classification number? How should classification searching and keyword searching work together? This article provides a practical guide to patent classification tools and how they support more complete patentability searches.

Why Patent Classification Tools Are Indispensable

A Classic Scenario

You need to search for “a method of removing contaminants from the surface of a semiconductor wafer using a laser”:

• One reference document might use “laser cleaning of semiconductor wafer surface”
• Another might say “laser ablation of surface contaminants in IC manufacturing”
• Yet another might say “removal of surface particles using pulsed laser irradiation on substrates”

All three describe the same technology, but if your keywords do not cover all of these expressions, you will miss relevant documents. Classification searching helps you cross the language barrier — regardless of what terminology an author uses, as long as the technology falls within the same category, it will be assigned to the same or a similar classification number.

IPC in Patent Classification Tools

What Is the IPC

The IPC (International Patent Classification), administered by WIPO, is the most widely used patent classification framework in the world. As of 2024, the IPC contains approximately 70,000 classification entries covering all fields of technology.

The Hierarchical Structure of the IPC

The IPC employs hierarchical classification, from the highest to the lowest level:

Section: B — Performing Operations; Transporting
│
├── Class: B60 — Vehicles in General
│   │
│   ├── Subclass: B60L — Electric Equipment or Propulsion of Electrically-Propelled Vehicles
│       │
│       ├── Main Group: B60L 50/00 — Electric Propulsion with Power Supply Within the Vehicle
│           │
│           └── Subgroup: B60L 50/50 — Using Propulsion Power Supplied Primarily or Entirely by Fuel Cells

Hierarchy Representation Rules:

• Main groups: Classification number followed by “00” (e.g., B60L 50/00)
• Subgroups: Classification number with specific digits (e.g., B60L 50/50)
• Hierarchical relationships among subgroups are indicated by indentation dots — the more dots, the lower the level in the hierarchy

IPC Applications in Patentability Searching

Advantages:

• Globally harmonized, suitable for multinational searching
• Free to access; all major databases support IPC searching
• Covers all fields of technology

Limitations:

• Relatively coarse granularity (approximately 70,000 entries compared to over 150 million patents globally)
• Slow update cycle (generally revised once per year)
• Inconsistency in classification quality across different patent offices

Search Syntax Example:

IPC=B60L50/50

Retrieves all patents under this classification number in Espacenet.

CPC in Patent Classification Tools

What Is the CPC

The CPC (Cooperative Patent Classification) was jointly developed by the USPTO and the EPO and represents a substantial expansion and refinement of the IPC. The CPC contains approximately 250,000 classification entries, and its classification granularity is far higher than that of the IPC.

CPC vs. IPC Comparison

A CPC example — refinement of the same technology from IPC to CPC:

• IPC: H01L 23/34 (Cooling arrangements for semiconductor devices) — a single entry
• CPC:
• H01L 23/34 (General)
• H01L 23/345 (Arrangements for cooling using bases or mountings having high thermal conductivity)
• H01L 23/367 (Using heat sinks)
• H01L 23/373 (Using specific materials for cooling)
• H01L 23/427 (Using liquid cooling)
• H01L 23/467 (Using forced air flow for cooling)
• H01L 23/473 (Using liquid flow for cooling)

The CPC allows you to pinpoint the specific cooling method rather than merely a generic “cooling” classification.

FI/F-Term in Patent Classification Tools

What Are FI and F-Term

The Japan Patent Office (JPO) maintains two proprietary classification tools:

FI (File Index): Based on the IPC but with extensive Japan-specific local extensions. The granularity of FI is higher than that of the IPC and is comparable to or finer than the CPC.

F-Term (File Forming Term): A complementary tool to FI that provides multi-dimensional indexing of patents from multiple “technical viewpoints” (such as purpose, function, structure, material, manufacturing method, etc.). This is a matrix-based rather than hierarchical classification framework.

Why Patentability Searches Cannot Ignore FI/F-Term

Japan is the third-largest patent-filing country in the world, particularly in fields such as automobiles, electronics, materials, and optics. Relying solely on IPC/CPC for searching Japanese patents may result in:

• An excessive number of hits that are difficult to filter
• Insufficient precision, leading to the omission of key prior art

FI/F-Term Search Channels

• J-PlatPat (Japan Platform for Patent Information): Free of charge; supports FI/F-Term searching
• Some commercial databases (such as Derwent and PatSnap Analytics) also integrate classification-based patent analysis workflows

Practical Example:
On J-PlatPat, use the F-Term “2H045” (the F-Term theme code for optical elements) combined with specific dimension codes to construct a search query.

How to Find the Correct Classification Number in Patent Classification Tools

Method 1: Start from Relevant Known Patents (Most Practical)

This is the most efficient approach in patentability searching practice:

1. Conduct an initial search on Espacenet or Google Patents using a few core keywords
2. Browse the returned patent list and identify 3–5 patents most relevant to your invention
3. Check the classification numbers in the bibliographic data of these patents (both IPC and CPC are typically listed)
4. Enter these classification numbers into the WIPO IPC search tool at ipcpub.wipo.int or the USPTO CPC search tool to review the definitions, scope, and hierarchy of the classification numbers
5. Confirm whether the classification number accurately covers your technical field; simultaneously review its parent classification number (broader) and child classification numbers (narrower) to determine whether a more suitable choice exists

Method 2: Use Classification Number Search Tools

• WIPO IPC Search: https://ipcpub.wipo.int — enter keywords as you understand them and see which IPC entries the tool recommends
• USPTO CPC Search: https://www.uspto.gov/web/patents/classification — browse the CPC hierarchical tree
• Espacenet Classification Search: built-in classification browsing functionality

Method 3: Industry Convention Approach

In long-term practice, certain specific technologies have “established by convention” core classification numbers:

• Lithium batteries: H01M 10/05xx series
• Wireless communications: H04W series
• Pharmaceutical compositions: A61K series
• Genetic engineering: C12N 15/xx series

Experienced patentability searchers accumulate a library of “core classification numbers” corresponding to these fields.

Strategies for Combining Classification Searching and Keyword Searching

Basic Principle

• First use classification numbers to define the technical field, then use keywords to focus on the specific solution
• Doing so ensures that you will not miss prior art in an entire technical field simply due to vocabulary differences

Combined Search Query Example

(IPC=H01L23/34 OR CPC=H01L23/373)
AND
(graphene OR carbon nanotube)
AND
(heat dissipation OR thermal management)

Iterative Optimization Process

1. Begin with a broad IPC main group search → Observe the characteristic classification numbers appearing in the returned documents
2. Narrow the scope based on characteristic classification numbers → Use CPC subgroups for precise searching
3. Apply a secondary keyword filter within the classification-locked document pool → Improve precision
4. If there are Japanese patent family members → Extract FI/F-Term numbers and conduct a supplementary Japanese search

Common Pitfalls in Classification Tool Searching

Pitfall 1: Assuming a Single Classification Number Is Sufficient

A single patent may have multiple IPC/CPC classification numbers, each indexing the technology from a different perspective. Searching only one classification number may miss patents in the same category that are indexed from other perspectives.

Solution: Review all classification numbers assigned to a relevant patent and incorporate all of them into the search scope.

Pitfall 2: Not Understanding the Hierarchical Relationships of Classification Numbers

Looking only at the textual description of a classification number without understanding its position within the classification tree. For example, H01L 23/34:

• It belongs under the main group H01L 23/00 (Details of semiconductor devices)
• Below it there are more refined subordinate classification numbers

Solution: Use classification number search tools to thoroughly browse the hierarchy of that classification number.

Pitfall 3: Using Incorrect IPC Search Syntax

• Different databases use different syntax for IPC searching. Some use IPC=, some use IC=, and some use CL=
• Pay attention to how forward slashes and spaces are handled

Pitfall 4: Assuming CPC Provides Global Coverage

Although the CPC is more refined than the IPC, not all national patents have complete CPC indexing. For patent documents from countries other than the EPO/USPTO, one should not rely solely on the CPC.

Key Takeaway: Patent classification tools (IPC/CPC/FI-F-Term) are essential tools for overcoming language differences and ensuring comprehensive patentability searching. The IPC is suitable for global initial searching (broad coverage), the CPC is suitable for precise deep searching (fine granularity), and FI/F-Term is a specialized tool that cannot be overlooked for Japanese patent searching. The optimal approach is a combined search strategy of “classification numbers to define the field + keywords to focus on the specific solution.”