Processors for desktop PCs communicate with the mainboard via up to 2000 contacts. So that this works reliably, there are high-precision interchangeable sockets.
Current x86 processors are connected to a mainboard by several hundred to a few thousand contacts. On the one hand they transmit signals with high frequencies, on the other hand strong currents. Over a hundred contacts ensure that a 140-watt CPU can draw more than 100 amps under full load.
CPUs in notebooks and tablets are mostly soldered; for desktop PCs and servers there are still interchangeable versions with around 900 (AMD FM2) to over 2000 (Intel LGA2011) contacts.
The images show the LGA1150 socket for Intel’s 4th and 5th generation Core i processors. The number in the designation refers to the number of contacts used. LGA stands for Land Grid Array, i.e. for contact areas (lands) that are arranged in a grid form (grid array).
touch of gold
The counterparts in the socket, also known as the CPU socket, are tiny springs. They are made of copper alloys with high resilience. In order to keep the transition resistance low and to avoid corrosion, the springs are nickel-plated and gold-plated. Intel specifies a minimum of 0.38 microns (15 microns) for the gold layer.
The shape and pressure of each contact spring ensures that its tip penetrates a tiny bit into the gold-plated contact surface of the processor as soon as the metal frame presses the CPU into the socket. Intel calls the lever mechanism provided for this purpose the Independent Loading Mechanism (ILM). So that their force does not bend the circuit board too much, the current LGA sockets have a metal plate on the underside of the mainboard.
Once the processor socket also served as a holder for the cooler, today these functions are separate: the cooler hangs on holes in the mainboard. The strong compressive force of the cooler brings the actual silicon chip of the CPU into close contact with the sheet metal cover attached above it. The latter serves as protection during assembly, but also distributes the heat from the CPU as an “Integrated Heat Spreader” (IHS).
Modern processors change their power consumption within a few milliseconds depending on the load. Consequently, the current also fluctuates quickly. The circuit for the CPU power supply is therefore very close to the socket, sometimes even in it and on the underside of the CPU between the contact surfaces: Mini capacitors soldered there iron out current peaks.
Gas and oil are getting more and more expensive. In c’t 20/2022 we therefore draw attention to cheap and ecological alternatives with and without replacing the heating system. We will also show you how to use the Raspi to protect yourself from trackers, test hacker tools, smartphones and graphics cards, and talk to Leica about cameras. You can read that and more in the current issue of c’t.