PCB Load

Category:  Surface Mount

Description: The PCB load process is the automated feeding of the assembly line by using a Bare Board Unstacker, or equivalent machine. A stack of bare PCBs is loaded into a magazine or directly onto the unstacker, depending on the specific unstacker model. A plunger may push the PCB into the line, or the PCB may drop from the stack onto the conveyor.

Major Cost Drivers -- PCBA PCB Load

PCB Load Cycle Time is the sum of time to unload the PCB from the stack of PCBs (Unstacker Time), the time to transport across the length of the unstacker machine (Transport Time ), and the time to reload the unstacker with a stack of PCBs (Reload Unstacker Time). Note that there is a weight and height limit of the stack that the machine can accept, therefore the Cost Model must look for the lowest integer between the maximum capacity based on height and the maximum capacity based on weight. Based on this capacity, we can determine how many times per batch the reload will need to happen and we distribute this time evenly across the batch, assuming that the impact of this time is only required to determine costing and is not critical to determine line balancing.

// Process Time for PCB unstacker to feed SMT line.

Process Time = Unstacker Time + Transport Time  +
(Reload Unstacker Time/Batch Size)

Time for one PCB to unstack.

  • Unstacker Time = (Machine variable)

    //Time for one PCB to unstack.

  • Transport Time = Unstacker Conveyor Length/Unstacker Conveyor Speed

    //Transport time through inspection station.

  • Transport Time = Unstacker Conveyor Length/Unstacker Conveyor Speed
    • Unstacker Conveyor Length = (Machine variable)
    • Unstacker Conveyor Speed = (Machine variable)

    // Time to reload stacker.

  • Reload Unstacker Time = (Roundup(Batch Size/Unstacker Capacity))*Reload Time
    • Unstacker Capacity = min(rounddown(Max Stack Height/PCB Thickness),
    • rounddown(Max Stack Weight/PCB Weight))
    • Max Stack Height = (Machine variable)
      • PCB Thickness = (Global Input)
      • Max Stack Weight = (Machine variable)
      • PCB Weight =(PSO)
    • Reload Time = (Machine variable)

User Inputs –- PCBA PCB Load

Process specific: N/A

Global Inputs: PCB Length, PCB Width, PCB Thickness, PCB Weight.