PCB Manufacturing Flashcards
Describe the steps to manufacturing a double sided PCB.
- Copper clad laminate board
2.Drill holes and debur - Electroless plating of holes to make conductive.
- Photoresist applied
- Apply surface finish for areas to be soldered.
- Apply solder mask.
What does a double sided PCB enable?
It allows the manufacture to place smt components on both sides of the PCB.
What is the most common PCB substrate material?
Glass reinforced epoxy “FR4”
What are the typical properties of PCB substrate?
- Stiff-provides mechanical support for the circuit.
- Temperature resistant - won’t become floppy when hot.
- Dielectric properties - Good insulator, low dielectric constant.
What is the main reason for PCB drilling?
It allows electrical connectivity between the top and bottom layer of the PCB.
It also allows connectivity between the different layers of a multi layer PCB.
What material are PCB drill bits made from?
Tungsten Carbide
What are drill registration holes used for?
To align multiple sheets.
What type of machine is used to drill pcbs?
Multi spindle Cnc drilling machine.
What purpose do entrance and exit materials serve when PCB drilling?
Minimise burring and improve accuracy.
What other manufacturing method can a PCB drilling machine carry out?
They can be used for routing a PCB board. (Cut out segments)
What alternatives are there to PCB drilling?
- Punching
- Moulding
- Photolithography
- Laser Drilling
What are the 3 types of lithography?
- imaging
- etching
- plating
What is the equation for exposure time?
Exposure time = sensitivity/intensity
What are the 3 most common exposure techniques?
- Contact exposure (the most common)
- Proximity printing
- Projection printing
Why is contact exposure the most common method used in lithography?
Accurate reproduction of image.
Low exposure tooling cost.
What is proximity printing and what type of light does it require?
It is similar to contact exposure, however a small gap is left between the tool and part.
The process requires collimated light - Light that has parallel rays.
What benefit does proximity printing have over contact exposure?
The artwork does not get damaged as easily.
Where is projection printing used?
High volume areas where high resolution and close tolerances are necessary.
What is the main downside of projection printing?
It is very expensive.
What aspect of the image has a large affect on the quality of the image transfer?
Contrast
Describe positive and negative resist
The resist is exposed to UV light. Then developed. The exposed metal is then etched away.
Positive = photo resist removed.
Negative = everything around photo resist removed.
How is the photo resist aligned on the PCB?
Precut alignment marks.
What does etching involve?
Removing copper material from PCB
What does isotropic etching mean?
Etching in all directions (horizontal and vertical)
What does anisotropic etching mean?
Etching In one direction only.
What methods could be used for dry etching?
Gas/plasma
What does plating mean, and what are the two methods of doing it?
Adding copper to a PCB.
Electroless
Electrolytic
What is the difference between Electroless and electrolytic plating?
Electroless is slow but can add copper onto other metals and insulators.
Electrolytic is fast but only works on conductive substances.
What is a side affect of isotropic etching?
Overhang under the mask
In what order would you use the two types of plating?
Electroless first, electrolytic second.
Describe pattern plating.
- mask off the majority of the PCB, leaving a small amount of copper.
- low current needed.
Describe panel platting.
The entire surface of the substrate is copper plated.
Lots of excess copper removed.
Larger current needed.
What is the benefit of having a multilayer PCB.
More circuit track per unit area
What is the purpose of a blind vias
Holes inside a multilayer PCB that link layers.
I’m what application would a flexible PCB be used for?
Wiring between parts of a system.
A PCB needing to fit into a small space of a product.
Can also be combined with rigid PCB’s.
