Resource-saving rework of printed circuit boards

The last step of manufacturing pcbs is to coat the surface finish. The surface finish prevents oxidation of the copper of the pcbs, which ensures a following processing actions of the pcbs (e.g. soldering, bonding, contacting or press-fit). If the pcbs are not processable after manufacturing, there are usually only two options as a result: to scrap the pcbs or to strip the surface finish and coat the pcbs again. Both options are very expensive and partially very harmful to the environment. A further aspect against the stripping and a new coating is the enormous stress which the pcbs are exposed to can lead to failure.

Currently a couple of reworks so called refresh processes are available. Hazardous chemicals are by far as far as possible not included in the process chemistry.

Which surface finishes can be reworked?

Why and When does pcb need to be reworked?
Basically pcbs need to be reworked, if:  

  • The solderability is not sufficient for multiple solder steps
  • The coating thickness is too thin (iSn)
  • The initial coating is insufficient (iSn, OSP)
  • The surface finish is deposited with copper / cementation
  • The surface finish is contaminated; ionic contamination >1.55 µg/cm² NaCl-Equivalent
  • The nickeloxide on the surface is diffused

How does the smarttin® refresh process work?
During the smarttin® refresh process, the copper contaminations of the intermetallic phase as well as the undefined tin oxides will be removed. In a parallel process a new pure layer of tin (>0.1 µm - max. 0.3 µm) will be deposited specially on the position where the copper was removed. This situation is called a “self-healing process”.

How does the ENIG/ ENEPIG post-treatment work?
In the FinalClean process, the nickeloxide on top of the surface of gold layer will be removed. The Sulfuric acid and Aurotech FinalClean will dissolve the nickeloxide with ultrasonic support. Afterwards the pcbs will be rinsed in a 4-step water cascade. This will lead to a perfect rinsing result. After rinsing the pcbs will get dried in a horizontal dryer.

How does the OSP refresh process work?
For the OSP refresh process the initial OSP layer must be removed form the pcb. Afterwards the copper will be etched ≤1.0 µm with a soft micro etch and the pcb must be coated again. The dissolving of the initial OSP layer and etching of the copper as well as the coating will be accomplished in horizontal mode of equipment. 

The technology of APL is in accordance with social-political guidelines for quality and environmental protection. APL wants and complies those high level guidelines through an active contribution of saving and improving resources of ground, air and water. Those three post-treatment processes enable a resource saving surface treatment which lead to an additional benefit for the customer and the environment.  The use of critical chemicals is not necessary for all three reworking processes.
Author: Mr. Dirk Kaschel

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