Electronic Engineering Drawing And Workshop

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

List of Practicals:

 

             Practical on making of Schematic diagram and Netlist generated on OrCAD V 10.0.

 

        Practical on the handling of layout, the component selection, placing, routing, DRC/ERC, CAM file generation in OrCAD.

 

          Introduction of the materials required, for the fabrication of    PCB’s, copper sheet cutting and measurements.

 

          Practical on the introduction of CNC software, the CNC machine handling for making PCB’s.

 

            Practical on plotting, fixing and developing a film for exposing of PCB’s.

 

             Practical on the Electroplating processes involved for making PCB’s.

 

         Practical on lamination, exposing and fixing of dry film on copper clad board for double sided PCB.

 

              Practical on the printing processes, Etching, Cleaning, Drilling involved in PCB

 

 

 

 

 

 

 

 

 

 

 

 

 

Introduction of the materials required for the fabrication of PCB’s.

 

Scope of Study

 

This practical covers the introduction of the different materials, equipment, and machines for the fabrication of a PCB.

 

Objectives

Upon the completion of this experiment, you will be able to:

1.                Know about the equipment, materials, tools and machines that are used for the making of PCB.

2.                Use these materials, equipment and tools for making of PCB.

 

Background:

The designer as well as manufacturers prefer to use both the imperial as well as non-imperial system of units.

The most important to remember are:

 

mil=inch by 1000

1 mil =25.4 micron

I micron =1 mm by 1000

 

Tracks on a PCB add inductance, resistance and capacitance to the circuit. The amount of inductance is relatively constant across substrate types and depends on the length of track. The inductance per unit length of copper track is similar to that for a component lead.1nH/mm.

Resistance of the track depends on the crossectional area of the track as well as the length, hence values are usually quoted in resistance per square for each weight of copper the most popular copper weight,1 oz., gives a typical value of 0.49mΩ /square.

 

Capacitance:

 

C=Є0ЄrA/h

 Where as Є0=8.854 pF/m

Єr =4.7 for FR4

A=coverage area

h =distance between tracks

Therefore a 1 oz. copper track, .5 mm (0.020 “) wide,20 mm(.8 “)long over a ground plane on a .25 mm(.010”)thick FR4 laminate would exhibit a resistance of 9.8 mΩ, an inductance of 20nH,and a capacitive coupling to ground of 1.66 pF. Thes values may seem like low and negligible but when we talk of so many track then these values add up. These parasitic effects are under designers control very muck like components values.

 

There are other design constraints like production, marketing cost etc.

Some important tables are given her for the ready reference and handy ,fast calculations

 

Laminate Material Properties:

 

Base material	Ref. Name	Relative dielectric constant(Єr)	Max. temp. Tmax (degree Celsius)	Thermal conductivity K(W/m per K)	Remarks
Difunctional epoxy	FR4	4.2—4.9	120--130	.18

 

 

Copper Track Properties:

 

Copper weight(oz.)	Track thickness(mm)	Track thickness(inches)	Track resistance(m ohms/square(1mm*1mm)

 

 

Observation:

 

Take a copper clad board.At first ,single side copper bard.Measure  and note the following parameters in it.

 

Base material	Ref. Name	Relative dielectric constant(Єr)	Max. temp. Tmax(degree Celsius)	Thermal conductivity K(W/m per K)	Remarks

 

 

Copper Track Properties:

 

Copper weight(oz.)	Track thickness(mm)	Track thickness(inches)	Track resistance(m ohms/square(1mm*1mm)

 

 

Show calculations also. Refer the background and other notes for the calculations.

 

Calculate the same tables for the double-sided board also. Compare the results of single-side and double-side boards. Note the difference.

Then compare your results with the standards given in the tables.

 

 

 

Summary

 

The availability of the copper plate of the proper size is the first and foremost requirement for the making of the PCB. In addition to it, you also require the precision high speed cutter blade for the fine and précised cutting of these copper plates to the required size. There can be the manual drilling machine for the drilling of the holes for components to be placed or the automatic plant as to the availability of the resources at your hand. There is the list of other equipment to add this like a personal computer printer, saw, scale, Photoplotter, screen printing facility, chemicals, chemical treatment plant for the exposing and lamination of the PCB.

 

Tests And Measurements

 

Measure the dia of the copper plate by the vernier caliper. Use the scale for measuring the area of the copper plate to be processed. Test check all the machines before making the start as all the machines are to be précised to your choice.

 

Preliminary Instructions

 

It is better to know about the each material, tools, machines and equipment etc.

Use the copper plates of the proper choice not to waste the copper plates as they are costly equipment.

Handle machines with the utmost care as they might be damaged as they are sensitive.

You might also hurt yourself while working on these machines.

 

Experimental Procedures

 

1.              Make a list of all the items that are to be introduced to you.

2.              Write brief introduction about the each item.

3.              Subdivide it into material, equipment, tool, machine, etc.

4.              Write about it’s usage as explained to you one by one.

5.              Use each of the items as explained to you by the instructor.

 

Review Questions

 

Complete the following statements with appropriate word or words.

1.    The copper plate is dia. Is measured and found to be ………(value) in (units of measurement).

2.    The instrument used for the measurement of length, width and dia were …,…. And …..

3.    The machine used for the cutting and drilling, were….,…..

4.    ….is better than …..for the drilling of the PCB.

5.    There is …layered,…layered, and ….layered PCB in the market.

6.  The list of the PCB softwares include…,….,…. and………softwares

 

 

 

 

 

 

 

 

 

Practical No.2

 

Practical on the identification of Drill Bits and Drilling on the Manual Drill Machine

 

Scope:

 

This practical starts with the introduction of various Drill Bits that are generally involved in the drilling of PCBs.The drill bit sizes are measured and then drilling is performed on a Drilling Machine.

 

Objectives:

 

Upon the completion of this experiment, you will be able to:

1.   know about the sizes of the different drill bits for drilling holes in a PCB.

            

2.     perform the drilling of holes of any suitable size on a PCB.

3.              

Background:

 

The drill bits come in different sizes as the boards vary in the size too.The drill bit can be less than a fraction of mm to any No. of millimeters.The mimimium size of the drill bit is related to the technology .If the technology is so précised than the drill bit size go on reducing to the limitations permitted by the resources at hand and the machinery involved.As the drill bit size is reduced and the automation is introduced so is the size increased.If some one wants to perform the drilling on the CNC (COMPUTER PNEUMATIC CONTROL )machine ,it is more précised ,specially in the working of IC pads.As the sizes involved are mils only.

So it also depends upon how you plan to go ahead.First of all ,the person who wants to drill must do sketches on the copper board if he is performing the drilling manually.If he is so précised at the handling of the machine than he can work without the skectching and can use any other method for getting the exact point where he has to drill a hole.

Normally the manuall machine has a motor attached to it that revolves around and there is a slot vacant for inserting the drill bit .There is a lever too ,that can be used to adjust the height of

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.

Manual drilling

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

• 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.

Through-holes

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 hole walls to prepare for through-hole plating.

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.

1.     Fully disassemble the drilled stack.

2.     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.

3.     Re-pin with the dowels and tape as before.

4.     Playing close attention to the drillmaster symbols representing the holes needed by the included substrate, drill the substack.

5.     Disassemble the substack and repeat steps 2 through 4 for each layer that needs further drilling.

6.     Inspect each layer after it is drilled and remove any debris that might be blocking the holes.

7. If all of the holes are drilled to your satisfaction, the individual layers are now ready for activation.

Summary

• 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.

Tests And Measurements

Minimium drill hole size,PCB thickness

Preliminary Instructions

1.ALWAYS WEAR SAFETY GLASSES WHEN OPERATING A DRILL PRESS, ESPECIALLY IF YOU ARE DRILLING WITH CARBIDE PCB DRILL BITS.

2.IF AVAILABLE, ALWAYS USE A VACUUM CLEANER TO REMOVE DEBRIS AND COLLECT AIRBORNE DUST DURING THE DRILLING OPERATION.

4.      THE DUST GENERATED DURING PCB DRILLING CAN POSE A VERY SERIOUS HEALTH HAZARD AND SHOULD NOT BE INHALED OR INGESTED UNDER ANY CIRCUMSTANCES.

Experimental Procedures

Through-holes

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 actvate the hole wall to prepare for through-hole plating.

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.

8. Fully disassemble the drilled stack.
9. 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.
10. Re-pin with the dowels and tape as before.
11. Playing close attention to the drillmaster symbols representing the holes needed by the included substrate, drill the substack.
12. Disassemble the substack and repeat steps 2 through 4 for each layer that needs further drilling.
13. Inspect each layer after it is drilled and remove any debris that might be blocking the holes.
14. If all of the holes are drilled to your satisfaction, the individual layers are now ready for activation

Review Questions

1.   Smallest workable drill bit size on the single-sided board is ……

2.   Largest workable size of the drill bit on the single-sided pcb is…..

3.   Smallest workable drill bit size on the double-sided board is ……

4.   Largest workable size of the drill bit on the double-sided pcb is…..

5.   The units for the size of the drill bits are…..

6.   TTL IC pad size is…..

7.   CMOS IC pad size is…..

8.   Resistor,capacitor,diode,inductor,transistor pad size is……

9. Percentage error for manual drilling is….

10.Variation in the drill hole size given to me during drilling is…..