Cleaning Copperclad Substrates

The proper cleaning of copperclad substrates is so important to the ultimate success of your PCB prototyping effort that it is understandably worth the effort to learn to do it well. Luckily, it is a process which is easily mastered given the ready availability of chemically optimized copper cleaners and easy to use cleaning tools. Be patient. It may take a couple of trial runs before you get it right. As your skill develops, you will find that this step goes quite rapidly and that your boards emerge uniformly clean, activated, and usable.

Equipment needed

• small sink or washtub with a spray wand if possible
• abrasive cleanser / copper brightener (scrub cleanser)
• abrasive scrub brush
• rubber gloves, safety glasses, and an old shirt or smock
• plastic cutting board (or 12" x 24" sheet of plastic)

Preparation

1. Thoroughly clean a work area adjacent to a utility sink
2. Clean the sink with a commercially available cleanser and insure that no residue remains that might contaminate the surface of the board. Since a number of the chemical cleaners used in PCB fabrication are mildly toxic, DO NOT USE A SINK THAT WILL LATER BE USED FOR FOOD PREPARATION. If a utility sink is not available, set up a stand with a plastic washtub and a source of hot water.
3. Have an approved eyewash handy in case you splatter some of the cleanser in your eye
4. Wipe down, and thoroughly rinse the cutting board (or sheet of plastic). Since this surface is where the copperclad will be cleaned, it is essential that it be as clean as possible.

Board cleaning

1. Spray both sides of the substrate with warm water to remove any loose grit.
2. Lay the substrate of the cutting board.
3. Sprinkle a liberal amount of scrub cleanser on one side and spread evenly with a slightly wet abrasive brush. The cleanser should form a loose slurry not a thin foam. The copper will immediately brighten upon exposure to the mild etchant in the cleanser.
4. Holding the board along one edge, scrub the surface using moderate to heavy pressure. A 2" (5cm) diameter circular wiping motion seems to work well and is less tiring than an equivalent linear motion.
5. Scrub the entire surface (except where your fingers are, of course).
6. Rotate the board 90° and repeat steps 3 and 4.
7. Continue in this fashion until the board has been rotated a full 360°. The intent of all of this diligent scrubbing and rotating is to impart a random pattern of shallow scratches to the surface of the board. Combined with the etching action of the cleanser, this abrasion will yield a chemically and mechanically activated surface that is ready for subsequent processing.
8. Flip the board over and repeat steps 2 through 6.
9. Flip the board back over to the first side and quickly wipe with the scrub brush to remove any discoloration that may have formed.
10. Very quickly rinse the board with warm water while lightly scrubbing both surfaces with the brush to loosen and remove any cleanser that might remain on the board.
11. Spray the board with cold water and carefully examine both sides. A properly cleaned and activated surface will support a uniform, break-free sheet of even the coldest water (cold water has much higher surface tension than warm or hot water). Any trace of beading or uneven sheeting may indicate surface contamination that will require further cleaning. Use your judgment. A perfectly cleaned board is not necessary for reliable PCB production, but an adequately cleaned one is. By and large, a good motto to use here is, "The Cleaner The Better (TCTB)" or "Anything worth doing is worth over-doing".
12. Once the board is cleaned to your satisfaction, blow dry with clean, dry, oil-free air and wipe both sides with a lint free cloth moistened with methanol (denatured wood alcohol).
13. Set the clean, dry copperclad aside until it needed. If the next step in the process is dry film lamination or multilayer lamination, it is a good idea to put the board into an oven for 5 minutes at 100°C to insure that all of the water is driven from the surface. This is also true if the board will be sitting for more than a couple of hours before further processing.

Clean up your work area!

• Thoroughly rinse the scrub brush and cutting board and set aside to drain. Always store both the brush and cutting board vertically to allow them to drain completely and to minimize the accumulation of airborne contaminants.
• Thoroughly rinse the sink. If you always leave your work area ready for the next use, PCB fabrication will flow more smoothly and your results will be more predictable.

Formatting Copperclad Substrates

Formatting refers to the process of assembling the copperclad substrates with backing and entry materials into a drilling stack and marking the entire stack in such a way that the orientation or each substrate is uniquely determined. In the case of a multilayer board, the layers must be stacked in the same orientation and order that they will occupy in the finished board. You must also determine beforehand whether your design will require blind or hidden vias, and establish a plan to drill these added holes in the proper layers. If you plan to make a number of multilayer PCBs, building a formatting template will save you a lot of work and help insure consistent results.

To some degree, the steps that you follow when stacking the substrates will depend on whether you will be drilling manually or have the use of an automated drilling machine.

For the sake of simplifying this discussion, the component side of the finished PCB will be referred to as the top and the solder side will be referred to as the bottom. The process for formatting and drilling a double-sided board is identical to the treatment of the inner layer.

Stacking

To get your layers ready for drilling:

1. Assemble the copperclad substrates into a stack wherein each substrate is in the same position and orientation (copper side up or copper side down) as it will be in the final PCB.
2. On the bottom of the stack, add a sheet of exit foil and piece of backing material (min. thickness = 0.08"). To the top, add a sheet of entry foil. Starting from the top, the stack should consist of: entry foil / top laminate / inner laminate / bottom laminate / exit foil / backing material
3. Backing material and entry foil, when used in conjunction with a pressure foot during drilling will virtually eliminate the formation of burrs on the top and bottom of the substrate. This is no minor consideration since copper is very ductile and tends to form long, difficult to remove cylindrical burrs around each hole. Entry foil (which is the same thing as exit foil) is also used on both sides of the stack to minimize cleanup after hole-wall activation.Tape the stack together by using four short pieces of masking tape angled across each corner.
4. In the middle of one side, about 0.25" (6.4mm) in from the edge, drill a 0.125" (3mm) dowell hole through the entire stack and insert a dowell pin until it is flush with the bottom of the backing material.
5. In the opposing side, offest from the middle of the side by at least 1" (3cm) and inset about 0.25" (6.4mm) in from the edge, drill another 0.125" (3mm) dowell hole through the stack and insert a dowell pin as before.
6. Make sure that both dowell holes are outside of the area to be occupied by your circuit pattern.
7. The reason for offsetting the second hole is to establish enough left to right asymmetry to insure that the stack can only be reassembled with the various layers in their original orientation. You could also do this visually by notching the same corner on each layer, but it is a lot easier to drill a hole off center than it is to cut or file FR-4.
8. If you will be using an automated drilling machine, the the stack is now ready for positioning on the drill table.

Mounting a drillmaster

If you intend to manually drill the stack, there is a further step that can significantly simplify the entire operation and give you a reliable visual check to make sure that all of the needed holes have been drilled.

1. Using adhesive label stock (e.g. "laser" labels or reprographic transfer film comprised of a paper or plastic printing surface, a layer of pressure sensitive adhesive,and a siliconized release liner), instruct your ECAD system to print or plot a 1 to 1 (100% scale) drillmaster.
2. It is very important that you determine the scales of both axes of your printer or plotter before printing the drillmaster (or subsequent artwork). These numbers should be used during the configuration of your ECAD software printer driver to insure that all printed / plotted output conforms to real world measurements; i.e. that a plotted inch is really equal to an inch plus-or-minus an acceptable tolerance (0.005" or 0.1mm max.)
3. Properly configured, a drill master will plot out the location of every hole in your board, using a unique symbol to represent each drill size. As such, it forms an excellent roadmap for manual drilling.
4. Peel off the release liner on the back of the adhesive and carefully apply the drillmaster to the entry foil on the top of your stack. Make sure that the "label" goes on without wrinkles or voids. Once the drillmaster is in place to your satisfaction, you are ready to manually drill the stack.

Remember that, if you are making a design that requires buried or blind vias, you will need to reserve unique symbols for each unique layer. As a matter of practicality, drill the through-holes first. It is then safe to pull the stack apart and assemble a substack containing the backing material, the layers that need further drilling, and the entry foil with the mounted drillmaster.

Note: If your design is small enough, or your label stock and printer format big enough, you can include the dowell holes drilled above in the drillmaster and mount it to the entry foil before assembling the stack. This has the advantage of locating the dowell holes with your PCB layout software where you can insure that the holes do not conflict with any circuit element or mechanical mounting holes.

Copperclad Substrates

Dielectric substrates that have been clad with copper foil are one of the basic "raw materials" of the electronics industry. Originally made of phenolic, they are now available in a variety of materials, and thicknesses. Selecting the right "copperclad" depends on the electrical, thermal, and mechanical characteristics that your application demands. Although there are some pretty exotic combinations to chose from, the vast majority of circuit designs can be tested and tweaked using substrates based on a glass/epoxy composite known as FR-4. Think & Tinker offers a selection of substrates, cleaning supplies, and entry/backing materials.



Cutting
Simple techniques for cutting and shaping copperclad substrates

Formatting
Preparing substrates for drilling and through-hole activation

Cleaning
Cleaning and activating copper foils

Blind or Buried Vias

Designs that use blind or buried vias (vias that do not penetrate through the PCB) need supplementary drilling operations before proceeding. Unfortunately, they are also quite a bit more difficult to activate and through plate since each must be processed singly.

• Fully disassemble the drilled stack.
• Reassemble a substack consisting of the backing sheet, one of the copperclad substrates that need additional drilling, and the entry foil that carries the drillmaster.
• Re-pin with the dowels and tape as before.
• Playing close attention to the drillmaster symbols representing the holes needed by the included substrate, drill the substack.
• Disassemble the substack and repeat steps 2 through 4 for each layer that needs further drilling.
• Inspect each layer after it is drilled and remove any debris that might be blocking the holes.
• If all of the holes are drilled to your satisfaction, the individual layers are now ready for activation.

Through-holes Drilling

1. Load the largest diameter bit to be used into the drill chuck, making sure that the depth ring is pressed firmly against the ends of the chuck jaws when they are fully tightened.
2. Using a piece of scrap backing material as a gauge, adjust the spindle travel stop on your drill press to a depth that insures that the entire tip of the drill bit penetrates at least half of the material's thickness. You can also use two pieces of entry foil as a "feeler gauge" to set the depth. Under no circumstances allow a PCB drill bit to drill into the table of your drill press. PCB bits are specifically designed to drill copperclad and will shatter if plunged into cast iron, steel, or aluminum.
3. Starting with the largest diameter drill bit, drill all of the through holes, stopping periodically to insure that the drill bit has not snapped off and that the spindle travel stop has not slipped.
4. As you drill each hole size (from the largest to the smallest) check off that diameter on the drilling chart. This is a good bookkeeping technique that will help you keep track of your progress and insure that no hole size is missed.
5. After all of the holes have been drilled, remove the backing material from the stack and reptape the remaining sheets with the dowel pins in place.
6. Hold the stack up to the light for visual inspection. Ascertain that all of the holes have been drilled through and that none are blocked by drill debris. If some debris is seen, remove by carefully pushing a smaller diameter drill bit through the hole.
7. If all of the holes in your circuit design go all the way through the board, you are now ready to activate the hole walls to prepare for through-hole plating.

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.

CNC drilling

The techniques for drilling copperclad for double-sided and multilayer PCBs with automated equipment are identical, with the exception that multiple drilling steps will be needed if your multilayer design includes buried or blind vias. Refer to the documentation that came with your drilling machine for more information (standard boilerplate cop-out). Items to remember include:

• set the STACK HEIGHT parameter to clear all dowel pins during traverse
• set the SPINDLE FEED (inches per minute) and SPINDLE SPEED (RPM) for each drill size to values consistent with drilling standard 0.062" (1.6mm) FR-4 copperclad.
• set the SPINDLE PLUNGE DEPTH so that the tip of the largest diameter drill bit fully enters the backing material. Otherwise, these large diameter holes will not totally penetrate to bottom laminate and exit foil.
• DO NOT contour route the board immediately after drilling the stack. This should only be done after all other processing is complete.

This machine is designed through the feature of heat inverter unit,it can finish drilling the hole of tubesheet、hole of bolt and drilling of sheet,also it can be used for handling of joint plate of steel construction and products etc.

• It has the system of clamp、automatic removal and refrigeration circulation.
• It has to to four power heads which makes it work high efficiently.
• Advanced CNC power head feed-in system.
• All kinds of safe monitor and alarm stop system:the machine will stop if the drill breaks or other contingency happens,in order to avoid mechanical failure.
• Easy operation,lower the possibility of misoperation and the affect of human factor to the quality of the machine.
• Realizing CAD/CAM(can be operated once the interrelated file is folded)