Ask the Experts
August 26, 2009 - Updated
August 23, 2009 - Originally Posted

Cutting inner layer circuits

What tools and techniques do you suggest for cutting inner layer circuits required due to engineering changes? Our circuit board are 8 layers. Do you recommend we use tools such as a Dremel drill? Should we use drill bits or some other cutting tool? We are concerned about operator control and potential damage to other internal circuits.

B. M.

Expert Panel Responses

Please insure all technicians are trained to the 7711 / 7721 rework standard and have proper certification training. The drills and techniques used in certification program outline the tools and techniques required to be successful. I did not see it mentioned in the write up question. The 7711 and 7721 is a five day certification course held at different sites around the U.S.A. This is a good course to insure repair capability and the type of skill level required.

Mark McMeen
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.

Cutting internal traces on bare circuit boards or assemblies can be completed utilizing a few different pieces of equipment. In all cases it critical to have a good set-up or fixture with the board firmly fixed flat. The process is generally outlined in the IPC 7711/7721 Repair Guidebook, see procedure 4.3.2 Conductor Cut, Inner Layer Conductors. We use both a milling machine with microscope set-up to view the cut location along with the depth control gauge to monitor the cutting process. We also use a benchtop precision drill system with a similar set-up.

The specific type cutter is also very important. An end mill will machine flat and use the outer edge of the cutting tool and that will work best. There are other factors to consider, such as review of artwork files to establish the best location for the cut, the fab drawing to understand the stack-up of the board so you are drilling to the proper depth, and test points to verify the cut has been completed.

Andy Price
Sales Engineer
Circuit Technology Center
Mr. Price has been a key member of the team at Circuit Technology Center since 1985. He has vast expertise, experience and understanding of complex circuit board rework, repair and modification operations. He is one of the most knowledgeable experts in this area across the globe.
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