The land grid array (LGA) is a type of surface-mount packaging for integrated circuits (ICs) that is notable for having the pins on the socket (when a socket is used) — as opposed to pins on the integrated circuit, known as a pin grid array (PGA).[1] An LGA can be electrically connected to a printed circuit board (PCB) either by the use of a socket or by soldering directly to the board.
The land grid array is a packaging technology with a grid of contacts, 'lands', on the underside of a package. The contacts are to be connected to a grid of contacts on the PCB. Not all rows and columns of the grid need to be used. The contacts can either be made by using an LGA socket, or by using solder paste.[2] The grid elements found in use can be e.g. circular, triangular or other polygonal shapes and might have even different sizes. Grids might sometimes appear like honey comb patterns. Designs are often optimized for factors like contact likeliness despite tolerances, electrical gap to neighboring contacts and for allowing best shapes for counterpart spring contacts including their outgoing electric connectivity to e.g. a backplane PCB.
LGA packaging is related to ball grid array (BGA) and pin grid array (PGA) packaging. Unlike pin grid arrays, land grid array packages are designed to fit either in a socket, or be soldered down using surface mount technology. PGA packages cannot be soldered down using surface mount technology. In contrast with a BGA, land grid array packages in non socketed configurations have no balls, and use flat contacts which are soldered directly to the PCB. BGA packages, however have balls as their contacts in between the IC and the PCBs. The balls are normally attached to the underside of the IC.
LGA has been used for high-end microprocessors and similar applications since the 90s, primarily in Unix workstations. These early uses predate the availability of modern LGA sockets, and instead used land grid arrays on both the processor package and the motherboard. An array of slightly compressible conductive columns held in a frame is then sandwiched between the two LGA surfaces and compressed using the heatsink. This was considered field upgradable by technicians at the time. Care had to be taken to not touch the conductive columns to avoid contamination.[3]
LGA is currently used as a physical interface for microprocessors of the Intel Pentium, Intel Xeon, Intel Core and AMD Opteron, Threadripper, Epyc, and newer Ryzen families. Unlike the pin grid array (PGA) interface found on older AMD and Intel processors, there are no pins on the chip; in place of the pins are pads of bare gold-plated copper that touch protruding pins on the microprocessor's connector on the motherboard. Compared to PGA CPUs, LGA reduces the likelihood of the chip being damaged either before or during installation as there are no pins that can be accidentally bent. By transferring the pins to the motherboard, it is possible to design the socket to physically shield the pins from damage, and the costs of installation damage can be mitigated as motherboards tend to be significantly cheaper than CPUs.[4]
While LGA sockets have been in use as early as 1996 by the MIPS R10000, HP PA-8000, and Sun UltraSPARC II[5] processors, the interface did not gain mainstream use until Intel introduced their LGA platform, starting with the 5x0 and 6x0 sequence Pentium 4 (Prescott) in 2004.[6] All Pentium D and Core 2 desktop processors use LGA 775 socket. As of Q1 2006, Intel switched the Xeon server platform to LGA, starting with the 5000-series models. AMD introduced their server LGA platform starting with the 2000-series Opteron in Q2 2006. AMD offered the Athlon 64 FX series on socket 1207FX through ASUS's L1N64-SLI WS motherboards. It was the only desktop LGA solution offered by AMD at the time until the release of Socket AM5 in 2022.
The most recent Intel desktop LGA socket is dubbed LGA 1700 (Socket H5), which is used with Intel's Alder Lake series Core i3, i5, and i7 families, as well as their lower-end Pentium and Celeron families. Their Skylake-X Core i7 and Core i9 families use the LGA 2066 socket. The LGA setup provides higher pin densities, allowing more power contacts and thus a more stable power supply to the chip.
AMD introduced its first consumer LGA socket, called Socket TR4 (LGA 4094) for its high end desktop platform Ryzen Threadripper processors. This socket is physically identical to their Socket SP3 for their Epyc server CPUs even though SP3 CPUs are not compatible with the desktop X399 chipset and vice versa.
The previous AMD server LGA socket was designated Socket G34 (LGA 1944). Like Intel, AMD decided to use LGA sockets for their higher pin densities, as a 1944-pin PGA would simply be too large for most motherboards.
