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back-process-flow.md [2026/05/07 16:13] – [Back end manufacturing definitions] arthurback-process-flow.md [2026/05/07 17:40] (current) – [Categorization] arthur
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   * **Foundries** (e.g., TSMC, Samsung Foundry, Intel Foundry) manufacture wafers based on customer designs.   * **Foundries** (e.g., TSMC, Samsung Foundry, Intel Foundry) manufacture wafers based on customer designs.
   * **OSATs (Outsourced Semiconductor Assembly and Test)** (e.g., ASE, Amkor, and JCET) handle packaging, encapsulation, testing, and final assembly.   * **OSATs (Outsourced Semiconductor Assembly and Test)** (e.g., ASE, Amkor, and JCET) handle packaging, encapsulation, testing, and final assembly.
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 This division of labor enables specialization but also fragments environmental accountability across borders and corporate entities. This division of labor enables specialization but also fragments environmental accountability across borders and corporate entities.
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 ## Back end manufacturing definitions ## Back end manufacturing definitions
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 {{ :elements.png?600|}} {{ :elements.png?600|}}
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 ### Connection between the die and the substrate ### Connection between the die and the substrate
  
-### Category of substrate +{{ ::fc_wire.png?300|}} 
 + 
 +The interconnection method between the die and substrate can also be of two types ((https://www.hqicsubstrate.com/ic-substrates-blog/show/flip-chip-vs-wire-bonding/)): 
 +  * **Flip Chip:** Modern method using solder bumps and underfill polymer on chip pads for direct interconnection between the die and the substrate ((https://en.wikipedia.org/wiki/Flip_chip)), 
 +  * **Wire Bonding:** Traditional method using fine wires (Aluminum, Copper, Silver, Gold) to connect die to substrate ((https://en.wikipedia.org/wiki/Wire_bonding)). 
 + 
 +Each method will have a specific process flow with different steps during the manufacturing in the fabrication plant.
  
 ### Connection between the substrate & the motherboard ### Connection between the substrate & the motherboard
 +
 +**CPU sockets** enable installation, replacement, or maintenance on motherboards, primarily used in desktops and servers. The socket is screwed directly into the motherboard. Since the socket and the substrate have to fit into each other, the choice of socket influence the choice of substrate. 
 +The two dominant types are ((https://www.pcba-manufacturers.com/lga-vs-pga/)):
 +   * **Land Grid Array (LGA):** uses flat contact pads (“lands”) on the package underside, aligned with matching PCB pads, and can be mounted via socket or surface-mount soldering, it has no solder balls, relying instead on direct solder or spring contacts for connection ((https://en.wikipedia.org/wiki/Land_grid_array)),
 +   * **Pin Grid Array (PGA):** is a square or rectangular integrated circuit package with pins arranged in a uniform grid on its underside for connection to a PCB, it relies on physical pins rather than solder balls or flat contacts ((https://en.wikipedia.org/wiki/Pin_grid_array)). 
 +
 +For the CPUs that will not be removed, the connection to the motherboard is done through the **Ball Grid Array (BGA)** method, it is typically used for laptops or smartphones where direct access to the CPUs is not useful. The BGA evolved from the PGA, replacing its grid of pins with solder balls on the package’s underside, which connect to matching PCB pads when heated and melted. During reflow, surface tension aligns the package precisely as the solder solidifies, creating reliable electrical and mechanical bonds ((https://en.wikipedia.org/wiki/Ball_grid_array)).
 +
 +{{ ::lga-bga-pga.png?600 |}}
 +### Categorization
 +
 +**Back end manufacturing** can be categorize between the following groups:
 +  * **LGA:** used by Intel for desktop CPUs. Pins are on the motherboard; CPU has flat contacts. Installation involves alignment and pressure.
 +  * **PGA:** used by AMD for desktop CPUs. Pins are on the CPU, motherboard has receptacles. Installation involves insertion.
 +  * **BGA:** used in mobile devices (laptops, tablets). CPU is soldered directly to the PCB via spherical solder joints. Non-detachable.
 +  * **FC-BGA:** more space-efficient; chip is flipped and soldered directly to PCB ((https://www.sinsmarts.com/blog/industrial-computer-cpu-packaging-methods-lga-pga-and-bga-analysis/)).
 +  * **WLP(Wafer-Level Packaging):** encapsulation occurs before wafer dicing, it is typically used for very small equipment such as headphones ((https://en.wikipedia.org/wiki/Wafer-level_packaging)).
 +
 +Other types of processes exists such as QFN, DFN ((https://en.wikipedia.org/wiki/Flat_no-leads_package)) which are not covered in the first project of naKnow.
 +
 +{{ ::typesencap.png?900 |}}
 +
 ## Full process flow for back-end manufacturing ## Full process flow for back-end manufacturing