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NEGATIVE ETCHBACK
Typically when a PCB is manufactured, Plated Though Holes (PTH) are manufactured through a process which begins with the laminate material containing the copper conduction land being drilled. After a number of intermediate processes, the drilled holes which are to be plated are cleaned (or desmeared). The process inherently causes the copper land to be recessed in from the edge of the hole walls.

The panel assembly is then put through a complex series of processes which sees the holes plated with copper and hence electrically and mechanically bonding to the copper land of the different layers within the PCB structure.

 

 

ETCHBACK (Positive)
While traditional Negative Etchback provides a cost effective and moderately reliable solution for the majority of applications, certain applications such as Military, Medical or Aerospace applications cannot afford to make this cost/performance trade off. In such applications where reliability is paramount, PTH holes manufactured with an Etchback (Positive) process is the solution.

This process causes the dielectric material in the hole walls to be etched back, causing the copper land to protrude out past the edge of the hole walls.

This enables the THP hole plating process to bond to up to three sides of the copper land, providing the greatest degree of reliability and immunity against metal fatigue due to mechanical stresses imposed by both external mechanical shock and thermal shock.

 

CONCLUSION:
Etchback relates to the relationship between the edge of the copper land and the edge of the hole wall prior to the plating process. While the majority of PCBs are manufactured using a Negative Etchback technique, which provides a cost affective moderately reliable solution for the majority of application, Etchback (positive) is seen as a better solution for applications requiring the highest levels of reliability.

 

 

 

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