Back-drill aluminum is a one-piece, margin-reserved coated entry sheet (0.16-0.19 mm) for the controlled-depth second pass in 5G and server PCBs. The single-unit construction eliminates the seam and delamination of laminated boards, giving tighter stub control (CpK at least 1.67 on 25/56/112 Gbps links) and less debris.
Key Takeaways
- Back-drill needs a dedicated entry sheet — standard entry boards can't deliver the stub control 5G/servers demand.
- One-piece + margin-reserved beats laminated structures for stub accuracy and yield.
- IPC-6012F (Section 1.4.3) now defines back-drill depth requirements — reference it for compliance.
What a Back-Drill Entry Sheet Actually Does
When you back-drill, the bit enters the panel a second time at a controlled depth. Without a dedicated entry sheet, the bit can wander, stub length scatters, and signal-integrity margin evaporates. A back-drill entry sheet: (1) locates the bit at the second entry point, (2) stabilizes the drill through the controlled-depth pass, (3) lubricates to reduce heat, and (4) maintains a consistent Z-reference so every hole meets stub-length target.
One-Piece + Margin-Reserved: Why It Matters
The one-piece design (aluminum base + coating as a single unit, with reserved edges) eliminates the seam/edge issues of laminated structures — no delamination at the edge, less debris, tighter stub control. The margin-reserved process also makes handling easier and reduces scrap.
Specifications at a Glance
| Parameter | Spec |
|---|---|
| Thickness | 0.16–0.19 mm |
| Construction | One-piece coated aluminum, margin-reserved |
| Application | 5G, server, communications, high-speed digital |
| Core benefit | Tight stub control → higher back-drill yield |
HW600 vs HW900 — Process Capability
| Grade | Base (mm) | Stub CpK | Best application |
|---|---|---|---|
| HW600 | 0.16 | ≥ 1.33 | Standard back-drill, cost-first |
| HW900 | 0.19 | ≥ 1.67 | Tight-tolerance, high-speed digital |
Applications
Back-drill sheets are specified wherever residual stub length threatens signal integrity:
Recommended Pairing
-8.webp)
FAQ
Why not reuse a standard entry board?
Standard entry boards aren't engineered for the second, controlled-depth pass — stub length scatters and yield drops. A dedicated back-drill sheet holds the Z-reference.
Which grade — HW600 or HW900?
HW600 for cost-first standard back-drill; HW900 where signal integrity demands tighter stub CpK (≥1.67) on high-speed digital.