ASTM B734
Standard Specification for Electrodeposited Copper for Engineering Uses
Specifies electrodeposited copper coatings for engineering uses such as underplating, stop-off, EMI shielding, and joining.
What ASTM B734 specifies
ASTM B734 covers functional electrodeposited copper rather than decorative copper or electroforming. Its classes directly state minimum thickness: Class 5, 12, 20, and 25 require 5, 12, 20, and 25 µm, while Class X uses a purchaser-specified thickness. The coating may serve as an engineering underplate, heat-treatment stop-off, EMI shield, joining surface, or buildup layer. A drawing should identify the class, significant surfaces, maximum buildup where fit matters, and any adhesion, porosity, solderability, or hydrogen-embrittlement requirement. Class number does not represent a corrosion-service severity.
ASTM B734 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Thickness | Requirement / test |
|---|---|---|---|
Class 5 | Engineering copper, 5 µm minimum. | ≥ 5 µm ≥ 0.2 mil | Thickness and adhesion. |
Class 12 | Engineering copper, 12 µm minimum. | ≥ 12 µm ≥ 0.47 mil | Thickness and adhesion. |
Class 20 | Engineering copper, 20 µm minimum. | ≥ 20 µm ≥ 0.79 mil | Thickness and adhesion. |
Class 25 | Engineering copper, 25 µm minimum. | ≥ 25 µm ≥ 0.98 mil | Thickness and adhesion. |
Class X | Thickness stated by the purchaser. | — | Specified thickness and agreed tests. |
Tests and the drawing call-out
Tests the document imposes
- Thickness
- Adhesion
- Porosity when specified
- Solderability by ASTM B678 when specified
- Hydrogen-embrittlement relief for susceptible steel
How to cite it
Drawing call-out
COPPER PLATE PER ASTM B734, CLASS <5|12|20|25|X>, <THICKNESS FOR X>, <SIGNIFICANT SURFACES>Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Finishes specified to ASTM B734
ASTM B734 — frequently asked
What does ASTM B734 Class 25 mean?
It requires at least 25 µm of copper on significant surfaces. It is a thickness designation, not a corrosion grade.
Does B734 cover decorative copper?
No. It is for engineering uses and excludes decorative copper and electroforming.
What is Class X?
Class X means the purchaser states the required thickness. The drawing should include both minimum and maximum values when fit is controlled.
ASTM B734 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗