The mPGA package is a micro pin grid array: a pin grid array built on a reduced 1.27 mm (50-mil) pin grid, half the pitch of the classic 2.54 mm PGA. Halving the spacing lets far more pins fit in a smaller body, which is why Intel used it for the 478-pin Pentium 4 (Socket 478, mPGA478B) after the older 370-pin package ran out of room. Below are the verified mPGA dimensions, the full list of mPGA and µPGA sockets, and how the format differs from standard PGA, LGA, and BGA.
Key takeaways
- The “micro” in mPGA is the pitch: 1.27 mm (50 mil) between pins, versus 2.54 mm (0.100 in) on a classic PGA (Intel mPGA478 design guidelines).
- Denser grid, smaller package: Socket 478’s mPGA478B fits 478 pins in a 36.5 mm substrate, where the older 370-pin Socket 370 needed 49.53 mm.
- mPGA (Intel’s term) and µPGA (AMD’s term) mean the same reduced-pitch PGA. AMD’s µPGA line ran from Socket A to Socket AM4.
- The pins sit in a regular array on mPGA478, not the staggered layout of Socket 370, and the socket is ZIF with a lever force capped at 4.5 kg.
- Same-size sockets are not interchangeable. Intel keys mPGA478A/B/C by which pins are depopulated, and mechanically identical mobile sockets are electrically incompatible.
- mPGA is a legacy desktop format. Socket 478 was Intel’s last desktop PGA; AMD’s last was Socket AM4, after which both moved to LGA.
What “micro” means in mPGA
mPGA stands for micro pin grid array. It is an ordinary pin grid array — pins on the package underside, plugged into a socket — but on a finer grid. Intel’s mPGA478 design guidelines specify a 50-mil (1.27 mm) pin pitch with a regular pin array, exactly half the 2.54 mm (0.100 in) spacing of a standard PGA such as Socket 370.
Halving the pitch is not cosmetic. It roughly quadruples the pin density per unit area, so a package can carry more I/O without growing. Socket 478 carries 478 pins in a 36.5 mm square substrate; the earlier Socket 370, on the coarse grid, needed a 49.53 mm body for fewer pins. Denser packages shorten traces and cut inductance, which matters as bus speeds climb.
The reduced-pitch idea did not stop at 1.27 mm. Mobile Intel Core i processors later used a reduced pin grid array (rPGA) at 1 mm pitch, and AMD held at 1.27 mm across its desktop line. mPGA sits in the middle of that progression: finer than classic PGA, coarser than rPGA.
[IMAGE 1: Side-by-side pin fields of a 2.54 mm standard PGA and a 1.27 mm mPGA, same area | alt: “mPGA 1.27mm pin pitch versus standard PGA 2.54mm pitch density”]
mPGA package dimensions
The canonical mPGA is Socket 478 (mPGA478B), the desktop Pentium 4 package. The numbers below come from Intel’s mPGA478 Socket Design Guidelines (order 249890-002).
| Parameter | Value | Source |
| Package example | Socket 478 (mPGA478B), Pentium 4 | Intel DG 249890-002 |
| Contacts | 478 | Intel §3.4.1 |
| Pin pitch | 1.27 mm (50 mil), regular array | Intel §1.1 |
| Pin array | 26 × 26 with 14 × 14 center cavity | Intel §2.2 |
| Pin length | 2.03 mm nominal | Intel §2.2 |
| Package substrate (max) | 36.5 mm × 36.5 mm | Intel §2.2 |
| Socket footprint (no lever) | 37 mm × 45 mm | Intel Table 3-1 |
| Socket height beneath package | 4.0 mm nominal (3.8–4.2) | Intel Table 3-1 |
| Contact base material | high-strength copper alloy | Intel §3.4.2 |
| Contact plating | 30 µin (0.762 µm) gold / 50 µin (1.27 µm) nickel | Intel Table 3-1 |
| Lever actuation force | ≤ 4.5 kg | Intel §3.8 |
| Contact current rating | 1.0 A/pin, Trise < 45 °C | Intel §4.10 |
| Mated loop inductance | < 3.3 nH | Intel Table 4-1 |
| Max mutual capacitance | ≤ 1.1 pF | Intel Table 4-1 |
| Mated contact resistance | ≤ 17 mΩ (Cu) / ≤ 25 mΩ (Kovar) | Intel Table 4-1 |
| Durability | 20 insertion cycles | Intel §5.4 |
| Package type | FC-PGA2 (flip-chip, with IHS) | Intel §2.2 |
The pin field is worth a closer look. It is a 26 × 26 array with a 14 × 14 block removed from the center, leaving a ring of pins around an empty cavity — the die and its capacitors sit in that gap. Pins are 2.03 mm long, on high-strength copper alloy, plated with 30 µin of gold over 50 µin of nickel in the contact zone.
[IMAGE 2: Underside of a Socket 478 mPGA478B package showing the 26×26 pin ring around the center cavity | alt: “Socket 478 mPGA478B pin field 26×26 array center cavity”]
mPGA vs standard PGA, FCPGA, LGA, and BGA
Pin pitch is the fastest way to place a PGA package. The table sorts the common formats by how the package meets the board.
| Format | Contact pitch | Contact type | Serviceable? | Example socket |
| Standard PGA | 2.54 mm (0.100 in) | pins | yes (socket) | Socket 370 |
| mPGA / µPGA | 1.27 mm (0.050 in) | pins | yes (socket) | Socket 478; AMD AM4 |
| rPGA | 1.00 mm | pins | yes (socket) | Socket G2 |
| LGA | package-specific | flat lands | yes (socket) | LGA1700 |
| BGA | package-specific | solder balls | no (soldered) | mobile Core i |
Two clarifications. First, “FC-PGA” describes how the die is attached (flip-chip), not the pitch — a flip-chip package can be standard-pitch or micro-pitch, so FCPGA and mPGA are orthogonal terms, not rivals. Second, LGA replaced pins with flat lands and moved the pins into the socket; it is where both Intel and AMD desktop parts ended up.
The mPGA and µPGA socket family
“mPGA” appears most on Intel’s Pentium 4-era sockets, but the reduced-pitch PGA format spans both vendors and two decades. The sockets below are all micro-pitch PGA.
| Socket (a.k.a.) | Vendor | Contacts | Notable CPUs |
| Socket 478 (mPGA478B) | Intel | 478 | Pentium 4, Celeron |
| Socket 479 (mPGA478A) | Intel | 478/479 | Pentium III-M, Pentium M |
| Socket M (mPGA478MT) | Intel | 478 | Core, Core 2 (mobile) |
| Socket P (mPGA478MN) | Intel | 478 | Core 2 (mobile) |
| Socket 604 (mPGA604) | Intel | 604 | Xeon (regular 1.27 mm array) |
| Socket A / 462 | AMD | 462 | Athlon, Duron, Sempron |
| Socket 754 | AMD | 754 | Athlon 64, Sempron |
| Socket S1 | AMD | 638 | Turion 64, mobile (1.27 mm) |
| Socket AM1 | AMD | 721 | Athlon / Sempron SoC |
| Socket AM4 | AMD | 1331 | Ryzen (Zen–Zen 3) |
Intel’s four mPGA478x sockets share a 478-pin, roughly 35 mm form factor but are not compatible: Socket 478, Socket 479, Socket M, and Socket P each move or depopulate pins. AMD’s µPGA line grew from 462 pins on Socket A to 1331 on Socket AM4, then stopped when Socket AM5 switched to LGA in 2022.
Keying and version traps
mPGA sockets that look identical often are not. Intel’s design guidelines define the mPGA478 versions by depopulated pins: mPGA478A removes pins A1 and A2, mPGA478B removes A1 and B1, and mPGA478C removes A1 and B2. A processor keyed for one version will not seat correctly in another.
The trap is worse across the mobile sockets. Socket 479, Socket M, and Socket P all use a 478-contact micro-pitch field, yet differ by the location of a single pin and are electrically incompatible. Confirm the exact socket designation, not just the pin count, before matching a CPU to a board.
Handling and mounting
mPGA is a ZIF package. Intel caps the actuation lever force at 4.5 kg, and the pins must be aligned before the lever is closed. The pins are fine and dense, so a dropped or mis-seated package bends them easily; a bent micro-pitch pin is far harder to straighten than a coarse PGA pin.
Each contact is rated for 1.0 A with a temperature rise under 45 °C (Intel mPGA478 guidelines), and the mated connection holds under 3.3 nH loop inductance and 1.1 pF mutual capacitance. Pin 1 is marked by a symbol or a corner notch on the socket; align it before actuating, because the dense field gives no second chance if the part goes in rotated.
Where mPGA stands today
mPGA is a legacy format on both sides. Socket 478 was the last Intel desktop socket to use a pin grid array; every Intel desktop socket since LGA775 uses land grid array. AMD kept PGA far longer, through Socket AM4 and its 1331 pins, but moved to LGA with Socket AM5 in 2022.
For a new design, you will not specify an mPGA CPU package — current desktop parts are LGA, and mobile and embedded parts are BGA. mPGA work today is identification, repair, and upgrade matching on Pentium 4-era and AMD-PGA systems. When you do, match the full socket designation and the keying, since micro-pitch sockets punish a wrong guess with bent pins.
Frequently asked questions
What does mPGA stand for?
mPGA stands for micro pin grid array. It is a pin grid array package on a reduced 1.27 mm (50-mil) pin pitch, half the 2.54 mm spacing of a classic PGA. The finer grid packs more pins into a smaller body. Intel’s Socket 478 (mPGA478B) Pentium 4 package is the best-known example.
What is the pin pitch of an mPGA package?
mPGA uses a 1.27 mm (50-mil) pin pitch, per Intel’s mPGA478 design guidelines, with the pins in a regular array. That is exactly half the 2.54 mm (0.100 in) pitch of a standard PGA. AMD’s µPGA sockets use the same 1.27 mm pitch; mobile rPGA sockets go finer, to 1 mm.
Is mPGA the same as µPGA?
Yes, in practice. mPGA (micro pin grid array) is Intel’s term and µPGA is AMD’s, but both describe a reduced-pitch pin grid array at 1.27 mm. Intel used mPGA on Socket 478 and its mobile variants; AMD used µPGA from Socket A through Socket AM4.
What is the difference between mPGA and PGA?
Standard PGA uses a 2.54 mm (0.100 in) pin grid, often staggered. mPGA halves the pitch to 1.27 mm on a regular grid, roughly quadrupling pin density. That let Socket 478 carry 478 pins in a 36.5 mm body, where a coarse-grid Socket 370 needed 49.53 mm for 370 pins.
Which CPUs use an mPGA package?
Intel’s Pentium 4 and Celeron (Socket 478, mPGA478B) and its mobile Pentium M, Core, and Core 2 parts (Sockets 479, M, and P) use mPGA. On the AMD side, the µPGA equivalent covers Athlon, Duron, Athlon 64, and Ryzen up to Socket AM4.
Is mPGA still used?
Not for new designs. Socket 478 was Intel’s last desktop PGA, replaced by LGA775, and AMD moved from PGA to LGA with Socket AM5 in 2022. mPGA remains relevant only for servicing or upgrading Pentium 4-era and AMD-PGA systems.
Bottom line
Treat mPGA as a micro-pitch PGA you will meet in old hardware, not a package you will design in. Its defining number is the 1.27 mm pin pitch — half the classic PGA grid — which is what let Intel and AMD pack hundreds to over a thousand pins into a hand-sized package before both moved to LGA. If you are matching a CPU to a socket, read the exact designation (mPGA478B, Socket M, Socket A, AM4), confirm the keying, and handle the dense pin field with care, because a single bent micro-pitch pin can scrap the part.
[IMAGE 3: The mPGA/µPGA socket lineage from Socket 478 and Socket A to AMD AM4, with pin counts | alt: “mPGA uPGA socket lineage Socket 478 Socket A AMD AM4 pin counts”]
External primary sources
- Intel Pentium 4 478-Pin Socket (mPGA478) Design Guidelines: https://download.intel.com/design/Pentium4/guides/24989002.pdf
- Wikipedia — Socket 478: https://en.wikipedia.org/wiki/Socket_478
- Wikipedia — Socket A (Socket 462): https://en.wikipedia.org/wiki/Socket_A
- Wikipedia — Socket S1 (1.27 mm pitch): https://en.wikipedia.org/wiki/Socket_S1
