PCB Via Lexicon: PTH, Blind, and Buried—No More Mix-Ups!

I still remember the day a Reddit user posted, “I always mix up blind vias and buried vias—help!” That single line sent me on a book-hunt through PCB design manuals and factory tour videos. After turning pages and turning heads on production floors, I distilled everything into this cheat-sheet so you’ll never confuse the three amigos again.
  1. The Skyscraper Analogy
    Picture a six-floor apartment block. Each floor is a copper layer, and the staircases are vias. The trick is knowing which floors each staircase connects—and whether you can see the staircase from the street.
  2. PTH – Plating Through Hole (The Classic Fire-Escape)
    • What it is: A drilled hole that runs from the roof to the basement, plating copper on its walls so every floor can hop on the same electrical “fire escape.”
    • How to spot it: Hold the board up to a lamp—if light shines through, it’s a PTH.
    • Pros/cons: Dirt-cheap to drill, but it hijacks real estate on every single layer, even those that don’t need the connection. Think of a fire escape bolted to floors 1–6 when you only live on 3 and 4.
    • Variants: PTH vs. NPTH (Non-Plating Through Hole). NPTH is just a mechanical hole—no copper, no connection.
  3. Blind Via – The Mezzanine Ladder
    • What it is: A staircase that starts on the ground floor (outer layer) and stops at the first mezzanine (next inner layer). From the sidewalk you can see the entrance, but you can’t see the exit—hence “blind.”
    • How it’s made: Laser or controlled-depth drilling after the core layers are laminated, or—more commonly—drill the outer layers first, then press them onto the core.
    • Pros/cons: Saves precious inner-layer real estate, but demands Z-axis accuracy and can drive plating headaches. Price sits between PTH and buried.
  4. Buried Via – The Secret Elevator
    • What it is: An elevator hidden entirely between two inner floors. From the street the building looks seamless, yet 3F and 4F have their own private lift.
    • How it’s made: Drill and plate the inner core pair (e.g., 3–4) before the outer layers are even glued on. After plating and imaging, the rest of the stack-up is laminated around it.
    • Pros/cons: Maximum space savings on HDI boards, yet the process is a wallet-thinning ballet of sequential laminations and registrations. Expect the highest cost per via.
  5. Quick Memory Hook
    • PTH = Public Through Hallway (everyone sees it).
    • Blind = Begins outside, ends inside—one side is blind to you.
    • Buried = Both ends are buried; you’ll never spot it from the street.
  6. Export Cheat-Sheet for RFQs
    When you next e-mail a PCB fab, paste this line:
    “Stack-up: 6-layer HDI, 1-2 & 5-6 blind microvias, 3-4 buried vias, all PTH non-functional on layers 2 & 5.”
    Your factory contact will high-five the screen.
  7. Bonus Pro Tip
    Always attach a via table and cross-section drawing. A picture saves a thousand e-mails—and a thousand mis-drilled holes.
Now you’re armed. The next time someone says, “Isn’t a blind via just a buried via with sunglasses?” you can share this link and watch them go from confused to enlightened—faster than a laser drill through FR-4.