The FCPGA package is a flip-chip pin grid array: a socketed processor package with pins on the bottom and a die mounted face-down on the substrate, its back left exposed so a heatsink presses on bare silicon. Intel introduced FC-PGA with the Coppermine-core Pentium III and Celeron for Socket 370, replacing the wire-bonded plastic PGA. The flip-chip attachment shortens the electrical path and puts the die within direct reach of the cooler. Below are the verified FCPGA dimensions, the FC-PGA versus FC-PGA2 split, and how the package compares to LGA and BGA.
Key takeaways
- FCPGA means the die is flip-chip bonded face-down to the substrate with C4 solder bumps, not wire-bonded. The die’s back faces up, exposed for the heatsink.
- The classic Socket 370 FC-PGA is a 49.53 mm (1.95 in) square, 370-pin package on a 2.54 mm (0.100 in) staggered pin grid, weighing about 7.5 g (Intel 2000 Packaging Databook).
- FC-PGA exposes bare silicon; FC-PGA2 adds an Integrated Heat Spreader (IHS), so the cooler contacts a metal lid instead of the die.
- It is a socketed package: pins enter a zero-insertion-force (ZIF) socket, and Intel specifies FC-PGA for ZIF only, not low-insertion-force sockets.
- The lineage runs FC-PGA → FC-PGA2 → micro-FCPGA (478-pin mobile) → rPGA (988-pin, 1 mm pitch mobile), while Intel desktop moved to FC-LGA lands and most mobile/embedded silicon is FC-BGA solder balls.
- Design it in only for service or legacy work; new desktop CPUs are LGA, and even AMD’s PGA (AM4) gave way to LGA (AM5).
What the FCPGA package is
FCPGA is a pin grid array in which the die is attached by flip-chip interconnect. In Intel’s construction, the die is bumped with controlled-collapse chip connection (C4) solder, flipped, and reflowed face-down onto an organic substrate; capillary epoxy underfill then fills the gaps around the joints (Intel 2000 Packaging Databook, FC-PGA assembly flow). The pins are Kovar, plated gold over nickel, soldered into the laminated substrate.
This is the opposite of the earlier plastic PGA (PPGA), which wire-bonds a face-up die to a copper heat slug. The difference shows on top: a PPGA presents a metal slug to the cooler, while an FC-PGA presents the bare back of the silicon die. Intel warns that on an FC-PGA, only the die should touch a conductive heatsink — not the pins, capacitors, or package edge.
Because the die is exposed, the cooler sits closer to the heat source, which is the point of the design. The trade-off is mechanical: bare silicon chips and cracks if a heatsink mounts crooked or over-clamped, a failure mode Coppermine and Tualatin builders learned by hand.
[IMAGE 1: Cross-section of an FCPGA package showing flip-chip die, C4 bumps, epoxy underfill, substrate, and Kovar pins | alt: “FCPGA flip-chip pin grid array cross-section C4 bumps underfill”]
FCPGA mechanical dimensions
The numbers below are for the 370-lead Socket 370 FC-PGA, the canonical FCPGA, taken from Intel’s 2000 Packaging Databook (Tables 13-2 and 13-8). The package meets JEDEC outline MO-128.
| Parameter | Value | Source |
| Package body (square) | 49.53 mm (1.95 in) per side | Databook §13.2.2 / Table 13-8 |
| Total thickness, excl. pins | 1.93 mm (0.076 in) | Databook §13.2.2 |
| Stack-up (pins + substrate + die) | 3.18 + 1.1 + 0.83 = 5.11 mm | Table 13-2 |
| Pin count | 370 | Socket 370 |
| Pin grid (nominal) | 2.54 mm (0.100 in), staggered SPGA | Table 13-8 (H) |
| Pin diameter | 0.43–0.48 mm (0.017–0.019 in) | Table 13-8 (φP) |
| Pin length | 3.05–3.30 mm (0.120–0.130 in) | Table 13-8 (L) |
| Pin material | gold-over-nickel-plated Kovar | Table 13-2 |
| Die footprint (max) | 19.84 mm (0.781 in) square | Table 13-8 (B1/B2) |
| Substrate thickness | 1.00–1.20 mm (0.039–0.047 in) | Table 13-8 (A2) |
| Package weight | 7.5 g | Table 13-2 |
| Thermal resistance θjs (with heatsink) | 0.6 °C/W at 12–15 lbf clip | Table 13-2 |
| JEDEC outline | MO-128 | Databook §13.2.2 |
| Pin-1 index | gold triangle (no chamfer) | Databook §13.2.2 |
Two details catch people out. First, the pin grid is a 2.54 mm (0.100 in) nominal array, but it is staggered (an SPGA), so nearest-neighbor pins sit closer and the socket is often described as 37×37. Second, there is no chamfered corner: pin 1 is marked by a gold triangle, so a part inserted by feel can go in rotated if the installer ignores the mark and the socket keying.
FC-PGA vs FC-PGA2: bare die or heat spreader
FC-PGA and FC-PGA2 share the pin field and socket but differ at the top. FC-PGA leaves the die back exposed; FC-PGA2 bonds an Integrated Heat Spreader (IHS) over the die, and the cooler contacts the IHS. Intel introduced the IHS as core power climbed near 1 GHz, then made it standard on Tualatin-core Pentium III and Celeron and on the Pentium 4.
| Aspect | FC-PGA | FC-PGA2 |
| Die / cooler interface | bare die back exposed | metal IHS over die |
| Heatsink contacts | bare silicon | integrated heat spreader |
| Die-damage risk | higher (exposed silicon) | lower (lid protects die) |
| Example cores | Coppermine PIII & Celeron | Tualatin PIII & Celeron; Pentium 4 |
| Socket | PGA370 | PGA370; Socket 478 |
| Introduced | with Coppermine FC-PGA | as core power neared ~1 GHz |
For anyone servicing old hardware, the visible tell is the top surface: FC-PGA shows a small bluish-tinted silicon die roughly 13 mm on a side; FC-PGA2 shows a metal lid covering the whole center. The IHS version is far more forgiving of heatsink handling.
[IMAGE 2: Side-by-side of an FC-PGA bare-die processor and an FC-PGA2 with integrated heat spreader | alt: “FC-PGA bare die versus FC-PGA2 integrated heat spreader”]
FCPGA vs PPGA, FC-LGA, and FC-BGA
These four families cover how a modern processor connects to a board. The interconnect type is the fast way to tell them apart.
| Package | Board contact | Die attach | Mounting | Typical use |
| FC-PGA | pins (male) | flip-chip (C4) | ZIF socket | PIII/Celeron, Socket 370/478 |
| PPGA | pins (male) | wire-bond | ZIF or LIF socket | Mendocino Celeron, Socket 370 |
| FC-LGA | lands (flat pads) | flip-chip | LGA socket | Intel desktop LGA775–LGA1700 |
| FC-BGA | solder balls | flip-chip | soldered to PCB | mobile Core i, embedded |
The pattern: PGA and LGA are socketed and serviceable; BGA is soldered and effectively permanent. FC-PGA and FC-LGA both flip-chip the die and differ only in whether the board contact is a pin or a flat land. Intel’s current desktop packages are all FC-LGA, from the Pentium 4 LGA775 era through LGA1700 (Intel package type guide).
Sockets and processors that use FCPGA
FCPGA is not one socket. The pin count and pitch grew as the lineage moved from desktop to mobile.
| Socket / package | Contacts | Pitch or size | Processors |
| PGA370 (FC-PGA / FC-PGA2) | 370 | 2.54 mm grid; 49.53 mm sq | PIII & Celeron (Coppermine, Tualatin); VIA C3 |
| micro-FCPGA (mobile) | 478 | pins 2.03 mm × 0.32 mm | mobile Pentium 4 / Celeron |
| Socket G1 (rPGA988A / FCPGA988) | 988 | 1 mm reduced pitch | mobile Core i (Gen 1) |
| Socket G2 (rPGA988B / FCPGA988) | 988 | 37.5 mm sq | mobile Core i (Gen 2/3) |
The desktop line ran on PGA370 and then Socket 478. Mobile parts kept pins longer: Intel’s micro-FCPGA uses 478 pins that are 2.03 mm long and 0.32 mm in diameter (Intel mobile package guide), and the later reduced pin grid array (rPGA), used for socketed mobile Core i3/i5/i7, tightened the pitch to 1 mm — finer than the 1.27 mm grid on contemporary AMD parts (Wikipedia, pin grid array). Socket G1 and G2 (FCPGA988) carry 988 contacts on a 37.5 mm body.
Handling, socketing, and thermal notes
FC-PGA is a ZIF-only package. Intel specifies zero-insertion-force sockets and single-lever actuation; the pins are aligned by hand, dropped in, then locked, with actuation force under 10 lb and no lubricant (Intel 2000 Packaging Databook). Do not force an FC-PGA into a LIF socket.
Cooling contacts the die directly on FC-PGA, so the thermal interface material must be electrically non-conductive and the heatsink must not bridge to pins or package metal. Intel gives a package thermal resistance near 0.6 °C/W with a heatsink at 12–15 lbf clip force. On FC-PGA2 the same rules apply, but the contact surface is the IHS, which spreads the load and removes the die-crush risk.
The keying matters. FCPGA pins are arranged so the processor inserts one way only, but a missing pin or a bent corner defeats that, so confirm the pin-1 triangle against the socket before you actuate the lever.
Where FCPGA stands today
FCPGA is a legacy desktop package and a shrinking mobile one. Intel desktop processors moved to land grid array with LGA775 and have stayed there through LGA1700, so a new desktop CPU is FC-LGA, not FC-PGA. Pins survived in mobile sockets (Socket G1/G2/G3, FCPGA988/946) and in AMD’s desktop line, where AM4 used a PGA with the pins on the chip — until AM5 switched AMD to LGA as well.
For a new design, you will meet flip-chip packaging as FC-LGA (socketed desktop) or FC-BGA (soldered mobile and embedded) far more often than FC-PGA. FCPGA work today is mostly identification, repair, and retro-system building. Match the socket (PGA370 vs 478 vs rPGA), the FC-PGA or FC-PGA2 thermal interface, and the electrical revision — a Coppermine and a Tualatin can share a Socket 370 body yet need different board support.
Frequently asked questions
What does FCPGA stand for?
FCPGA stands for flip-chip pin grid array. It is a socketed processor package with pins on the underside and a die flip-chip bonded face-down to the substrate, leaving the die’s back exposed on top for a heatsink. Intel introduced it with the Coppermine-core Pentium III and Celeron for Socket 370.
What is the difference between FC-PGA and FC-PGA2?
Both use the same pins and socket. FC-PGA leaves the silicon die exposed, so the heatsink touches bare silicon. FC-PGA2 adds an Integrated Heat Spreader (IHS) over the die, so the heatsink touches a metal lid instead. FC-PGA2 protects the die and appeared on Tualatin-core parts and the Pentium 4.
Is FCPGA the same as Socket 370?
No. Socket 370 (PGA370) is the 370-pin motherboard socket; FC-PGA is one package that fits it. Socket 370 also accepts PPGA and FC-PGA2 packages. The difference between PPGA and FC-PGA support is electrical, tied to voltage-regulator and pin-usage changes, so not every Socket 370 board runs every chip.
What is the difference between FCPGA and FCBGA?
FCPGA has pins that plug into a socket, so the chip is removable. FCBGA (flip-chip ball grid array) has solder balls reflowed onto the board, so the chip is permanent. Both flip-chip the die; they differ in the board connection — sockets for pins, soldering for balls.
What is the pin pitch of an FCPGA package?
The Socket 370 FC-PGA uses a 2.54 mm (0.100 in) nominal pin grid, arranged as a staggered array, per Intel’s 2000 Packaging Databook. Later reduced pin grid array (rPGA) mobile packages tightened the pitch to 1 mm. Pins are gold-over-nickel-plated Kovar, roughly 0.43–0.48 mm in diameter.
Are FCPGA processors still made?
Not for new desktops. Intel desktop moved to FC-LGA (land grid array) with LGA775 and stayed there, and AMD moved from PGA (AM4) to LGA (AM5). Flip-chip pins persist in some mobile and embedded sockets, but most current CPUs are FC-LGA (socketed) or FC-BGA (soldered).
Bottom line
Reach for FCPGA knowledge when you are identifying, servicing, or restoring a socketed processor rather than specifying a new one. If the die back is bare silicon, it is FC-PGA and the heatsink mounts to the die directly — handle it carefully, use a ZIF socket, and keep conductive material off the pins and edges. If a metal lid covers the center, it is FC-PGA2 and far more robust. For anything current, expect the flip-chip die to arrive as FC-LGA lands or FC-BGA balls; the pin grid array is now the exception, not the rule.
[IMAGE 3: Comparison of FC-PGA pins, FC-LGA lands, and FC-BGA balls on the package underside | alt: “FCPGA pins versus FCLGA lands versus FCBGA balls underside”]
External primary sources
- Intel 2000 Packaging Databook, Chapter 13 (Pinned Packaging): https://www.intel.de/content/dam/www/public/us/en/documents/packaging-databooks/packaging-chapter-13-databook.pdf
- Intel Package Type Guide for Desktop Processors (FC-PGA / FC-LGA): https://www.intel.com/content/www/us/en/support/articles/000005670/processors.html
- Intel Mobile Processor Package Types (micro-FCPGA / FCBGA): https://www.intel.com/content/www/us/en/support/articles/000006761/processors.html
- Intel Pentium III Processor for the PGA370 Socket Datasheet: https://download.intel.com/design/PentiumIII/datashts/24526408.pdf
