Retronix Blog

Nov 22, 2017

Connecting odd size components to a PCB, for R&D purposes.


Often it is required to test an IC while it is “in situ” i.e. placed on a working PCB.

To do this the IC has to be safely removed from the working PCB, placed on an interposer PCB which has connections to measuring equipment to measure it’s performance, then reconnected to the original PCB.

The problem often is that the interposer PCB will be bigger than the IC, so wont fit onto a tightly packed PCB. It has to be raised higher than the PCB in order to connect it.

Below is the traditional method on the left, and the newly developed Retronix method on the right, which has many advantages –

 

    • Original IC is removed using top heat (possibility of damage)
    • IC is reballed using reflow cycle
    • Grypper socket is soldered to the PCB to achieve height
    • Another gripper socket is soldered to the interposer pcb, to allow the reballed BGA to be mechanically connected to avoid too many reflow cycles causing potential damage
    • Interposer pcb is then mechanically connected to the first gripper socket
    • The IC under test is then mechanically connected to the interposer PCB gripper socket
    • Test is then carried out

     

The disadvantages of this process are :

  • Multiple reflow cycles on IC and PCB could cause damage and give incorrect data
  • IC is connected via 2 mechanical connections and 2 soldered connections, possible causing a communication issue possibly causing a data transfer issue.

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Interposer Rework

 

  • Original IC is removed using safe heat from underneath (Click Here)
  • IC is reballed using laser, avoiding reflow cycle (Click Here)
  • Solder spheres are attached to the interposer in a column, achieving the standoff height required (Click Here)
  • IC soldered to interposer using low temperature solder, and the interposer PCB connected to the original PCB using the same method
  • Test is then carried out

 

  • The advantages of this process are :

      • No loss of signal due to mechanical connections, only solder connections
      • No time delay or cost waiting on matching gripper sockets, solder ball columns instantly created
      • No dangerous reflow cycles to cause damage

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