The challenge on HDI lines
Microvias are drilled at high rpm into very thin dielectric. A few microns of drift and the via misses the target pad. Exit burr, even at 20 µm, breaks the electrical connection on the next layer.
Three failure modes dominate:
- Location drift — the bit walks on entry, the via lands off-pad.
- Exit burr — smeared copper at the hole bottom, caught only at electrical test.
- Resin smear — soft backup transfers resin into the hole wall and hurts plating.
Why the material stack decides the result
The entry board sets the bit. A coated aluminum first-entry holds the drill on centre and pulls heat away, so the first 0.1 mm is dead straight. The backup board then controls the exit: a dense, smooth-faced phenolic or UV melamine backs the hole so the last fibre breaks clean.
With the matched set we typically see:
- Hole location held within ±25 µm on Ø0.10–0.15 mm vias
- Exit burr reduced to ≤0.05 mm, often below the AOI threshold
- Resin smear low enough that mild desmear restores the wall
Grade matrix
| Board |
Grade |
Best for |
Exit burr |
| Lubricant Alu |
Green thermoset-coated (thermoset 220°C) |
Sub-Ø0.15 mm vias, HDI 1–2 step |
— (entry, default) |
| Backup |
UV Melamine 950 |
Standard HDI, 1–2 step microvia |
≤0.05 mm (default) |
| Backup |
Phenolic PHE |
Specialty — IC substrate / routing |
Available on request |
Services that shorten your evaluation
Free samples of the full HDI set are shipped in 5–7 days. A one-page comparison against your current supplier grade is returned with the samples. DFM advice in English and Chinese is included at no cost.
📖 Further reading: Case Study: Indian HDI Manufacturer Scaling Microvia Production · HDI & Micro-Via Drilling Material Selection Guide · Glossary: HDI definition →
FAQ
Q: Which backup for 1-step HDI at Ø0.12 mm?
A: UV Melamine 950 is our recommended default; 880 is the workhorse for standard HDI. Move to 950 when the core is thinner than 0.10 mm or the stack is above 10 L.
Q: Can coated aluminum replace a pure lubricant film?
A: Yes. Our thermoset 220°C coated sheet carries the lubricant and the entry stiffness in one piece, which is why it is a direct Coated alternative.
Q: Do you supply IC substrate grades?
A: Phenolic PHE is built for IC substrate drilling below Ø0.10 mm and is available on request. For most lines we recommend UV Melamine 950 as the default backup.
