Micro Via and Flex Circuit Panels
Micro Vias – Generally described as a via or hole through one or more layers of a flexible circuit board made of laminations of alternating insulating and conducting layers of material. These materials are often copper sheet (1/2 oz typically) and an epoxy/fiberglass blend in thin sheets (.001-.002” thick). The laser drilling tool will create a via from the top layer down to a copper catch pad below. This via will be plated to form an electrical connection between conducting layers.
The drilling and subsequent plating works best when the diameter of the via is equal to or greater than the depth of the via (a 1:1 ratio is ideal). Accu-Tech regularly generates vias in the range of .003” to .008” (.075-.100mm). There is capability to produce smaller and larger sizes.
For helpful links to information on the PCB industry, check the IPC website
Targeting and aligning
Our systems can align to pre-etched openings in the top layer and remove the dielectric down to the next layer. Likewise, we can create openings in a solid copper top layer aligned to your lower layer registration fiducials and then remove the dielectric. Supplying pre-etched openings in the top layer maybe more cost effective – depending on your etching capabilities. Pre-etched boards can have a quicker turn around time as well.
Registration targeting is usually a set of four “butterfly” targets, one at each corner of the panel just outside of the pattern of the part or parts. The supplied computer files (usually gerber or .drl format) will show the relationship of the targets to the via pattern. As well, this allows our systems to compensate for the slight shrinkage and out of square conditions that can be an outcome of the lamination process.
Furthermore, any overhanging or excess copper flashing from lamination should be pre-trimmed from the boards before delivery as this excess material can prevent the boards from laying flat on the laser tooling. As a result, this will increase consistency of features across a panel.
Guidelines for Via Drill Files:
1) We can accept .DRL files (ideal), Gerber or .DXF files.
2) Files must have different via sizes called out as different tool numbers all in the same file. One file per side/layer.
3) Fiducials should be identified as a separate tool number as well. We prefer these targets to be under .020” in diameter and can be of the butterfly, bulls-eye, circular pad or cross-hair type.
4) It is helpful to include tooling holes or landmarks to help quickly identify panel orientation.
5) Please send a panel stack-up showing the thickness of materials we are drilling through and landing on. This will help us in reducing the time for test patterns which reduces cost to you.
The laser is an excellent tool for precision separation of circuits generated in an array on flex panels. The laser’s very small ‘tool size’ as well as no contact forces may be very beneficial to either small part size or parts with chip components already attached.
Finally, our lasers generate very little smoke or carbon deposits on the edges of the parts therefore reducing cleaning time on your end. Our fixturing prevents parts from dropping or displacing after the final cut reducing risk to fragile parts. For additional cost, we can accommodate flexible circuits with stiffeners and/or components applied. In most cases, we can hold flex circuit accuracy to +/- .001”.