Manual Drilling

With the laminate stack formatted as detailed above, manual drilling is a straightforward, if somewhat mind-numbing process. Items to consider include:

• ALWAYS WEAR SAFETY GLASSES WHEN OPERATING A DRILL PRESS, ESPECIALLY IF YOU ARE DRILLING WITH CARBIDE PCB DRILL BITS.
• IF AVAILABLE, ALWAYS USE A VACUUM CLEANER TO REMOVE DEBRIS AND COLLECT AIRBORNE DUST DURING THE DRILLING OPERATION. THE DUST GENERATED DURING PCB DRILLING CAN POSE A VERY SERIOUS HEALTH HAZARD AND SHOULD NOT BE INHALED OR INGESTED UNDER ANY CIRCUMSTANCES.
• When using a conventional drill press, hole placement accuracy can be improved and drill breakage minimized through the use of a "sensitive drilling" or "finger" chuck. Small format, precision high-speed drill presses, ideal for PCB fabrication, are also available from a number of sources.
• Regardless of the type of drill press being used, a pressure foot should be employed if available.
• If available, position a work lamp on a flexible mount as close to the work surface as possible.
• Although more brittle than conventional high speed steel (HSS) drills, tungsten carbide bits designed specifically for PCB drilling will yield far superior hole wall quality. minimize burr formation, and outlast HSS bits almost 10 to 1. The downside is that, with smaller diameters [0.018"(0.46mm) and less], the carbide drills are easier to break and must be handled carefully.
• Always use drill bits that have been fitted with depth setting rings. This will allow you to set the plunge depth stop on your drill press to a single value that will work for all bit diameters.
• Prepare a chart that links the various diameter bits with the symbols used in the drillmaster.

The laquer (photo-resist) on the copper tracks may be used as a protective cover to prevent oxidisation of the copper during storage and also gives a little mechanical protection during drilling / handling. Ialways leave the resist on the PCBs until the PCB is drilled and needed for use.

Drilling should always be done with a high-speed drill and very little force should be applied to the drill to press it through the board. Do ing so would cause the drill bit to become blunt prematurely, especially if drilling fibre-glass PCBs. It will also cause a rough edge to the board where the drill bit comes through the board. Use good sharp drill bits. Use a stable drill instrument.


There are many hand-held modelers drills on the market in the US$20 region, but for about US$50 you can buy a decent 'drill press' (pillar drill / upright drill / bänkbormaskin) which has the advantage of not snapping drill bits. 0.7mm drill bits cost me over US$2 so a saving of only 25 drill bits paid for my drill press. For general PCB work I use 1mm drill bits because they are both heaper and easier to mount components.


The artwork must be so designed that the pads are bigger than the holes that are to be drilled in them. The artwork should also leave a 0.5mm hole in the center of each pad to guide the drill bit when the board is drilled. A high speed drill can throw fine particles which can damage eyes. Always use some form of protection, whether it be spectacles / goggles or a protective shield attached to the drilling machine. The work should also be well illuminated to help you drill the holes inthe correct places.

ERRORS

• Drill bit wandering with small or absent etched guide hole.
• Moving the board or drill during drilling can break drill bits.
• Using the wrong drill bit for the job.
• Injury to eyes - use protective shield or spectacles.
• Drilling the wrong places - use good lighting and count the holes.
• Forgeting holes - drill from one end of the board to the other. Count the holes.