Build A Board In-House Without The Mess

March 31, 2005
Novel technology moves pc-board prototype creation into the office.

When I built my first pc board, I taped up a copper-clad board and dropped it in a tub of etchant. While pc-board production hasn't changed much since then, dozens of companies now provide fast turnarounds for prototypes and small production runs. These new products provide an alternative to farming out this messy process.

Now along come the ProtoMatS62 and Pro-Conduct, which represent a far cry from my earliest efforts. The solution, developed by LPKF Laser and Electronics, comprises two parts. The ProtoMat62 removes the copper, and ProConduct fills in the holes, or rather, plates the holes.

Multilayer boards are built in the usual fashion, by stacking a set of boards. ProConduct is then applied to the stack. The process is fast and clean, making it possible to create boards in-house.

In-house pc-board generation offers a number of advantages. It significantly reduces turnaround time, speeding up time-to-market for the final product. Also, it can boost productivity by maintaining project momentum, because changes and fixes can be incorporated quickly. In fact, a board often can be completed in the time it takes to process a purchase order for an off-site pc-board service.

Often, the number of prototype boards created can be reduced for a particular run, because it's easy to make more. Designers also can try more prototypes. Making one board is faster than making two with this process, whereas it's just as fast to make many boards via the conventional process. Unfortunately, the conventional process is messy and has a much longer turnaround time.

Another major reason why companies prefer in-house pc-board creation concerns security and proprietary requirements. LPKF's approach makes this possible at a lower cost and with minimal fuss.

VERTICAL SIDEWALLS AND MORE The ProtoMat S62 is a plotter milling machine designed to very tight tolerances. Milling creates very precise, vertical sidewalls compared to etching (Fig. 1). Consistent vertical sidewalls can be quite beneficial in high-frequency RF designs. In fact, the S62 could be used on just the RF portion of a board built via conventional means (Fig. 2).

An optional vacuum table on the S62 holds the board in place (Fig. 3). Thus, the device can handle a variety of materials, from flexible circuit boards to plastic boxes. Yes, the S62 isn't restricted to making pc boards. It also can generate masks, panels, and even boxes that hold the electronics. Remember, this is a milling machine with a Z-axis movement, not just a pc-board generator. The Z-axis support may come in handy for cutting pockets in microwave boards.

The cutting head contains a light and vacuum intake, letting designers see what's going on. The vacuum intake moves the debris into a holding tank. System resolution is as fine as 0.25 µm (0.01 mils) with a milling-head travel speed of 150 mm (6 in.) per second.

The high-performance, 62,000-rpm spindle motor software control is designed to extend the motor's life by controlling how fast it ramps up and down when cutting.

The S62 comes with CircuitCAM and BoardMaster software, which can be used by itself or in conjunction with most CAD and pc-board creation programs. LPKF's software accepts formats such as Gerber, GerberX, DXF, HP-GL, ODB++, and Excellon.

Creation of both single and multilayer boards is possible with the S62. An optional fiducial recognition camera system automates front-to-back and multilayer alignment by locating fiducials embedded in a board design. The ProConduct technology provides plated through-hole support for double or multilayer boards.

PLATED THROUGH HOLES The ProConduct system is designed to create plated through holes without resorting to electroplating. The approach starts by applying an adhesive foil to both sides of a board and then drilling the holes that will be plated (Fig. 4). Application of a conductive epoxy paste follows in a method of placing the board on a vacuum table, applying the paste, and pressing it through the holes (Fig. 5). This occurs for both sides of the board. After that, the foil on both sides is removed (Fig. 6).

Next, the board is placed in an oven for about half an hour (Fig. 7). At this point, the board can be populated. The conductivity of hole plating is nearly as good as the electroplated approach, and ProConduct is significantly cleaner and easier to use. Typical resistance is 20 to 60 m(omega). The minimum size hole is 0.3 mm.

Plated through holes for multilayer boards are done in the same fashion as double-layer boards. However, the layers are stacked before the adhesive foil is applied.

The basic S62, including cabinet and tool change, costs just under $18,900 in North America. The optional automatic fiducial camera system and vacuum table are $4200 and $1750, respectively. The complete system comes in under $25,000. ProConduct starts at under $4000.

While the price is a bit high for very small operations, it's a bargain for designers who regularly prototype systems or generate small runs of custom boards. It also lets designers experiment and quickly fix errors with a new board instead of trying to patch a bad design.

Additionally, the S62 can be used to customize boards that it creates or boards from conventional pc-board processes. With custom boards, the S62 would be programmed to copper from only part of the board. This approach is very useful in customizing RF boards, allowing vendors to maintain a smaller inventory of a basic board design.

Firms that create prototypes will be interested in the S62 for small runs and fast turnaround. The process can be managed by any trained technician or even by the board designer. Further, this new approach makes it possible to try out one or more prototypes per day instead of one every two days. In fact, it is often possible to get a board done in the time it takes to process an invoice in may companies.

LPKF Laser and


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