Commercial PCB production Flashcards
Describe the stages in ‘flow soldering’
REMEMBER THIS SECTION IS ABOUT COMMERCIAL METHODS NOT WHAT YOU DID IN SCHOOL
- ‘Through hole’ components are placed into position on the PCB
- Board is fed into machine, either singly or in small batches
- Usually passes over a degreasing/cleaning stage (sometimes done by hand before being put into machine)
- Board passes over a heater to ‘pre- heat’ the tracks and components
- Board passes over a ‘wave’ of molten solder which joins components to the pads on the board
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Describe the operation of a ‘pick and place’ robot
- Used for mass production of commercial circuits that use very small ‘surface mount components’
- The machines has ‘tapes’ of components fed from all sides, as well as more complex components in trays
- Machines ‘picks’ up the components and ‘palces’ it onto the correct position on the board
- More complex machines can have many ‘heads’ dealing with several components at once
- Some can place as many as 20,000 components per hour
- The machines require lots of programming and testing before they can be used at full speed
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What are discrete components
Components that are usually handled individually such as resistors, transistors, capacitors rather than integrated circuits (chips) that contains lots of very small components
More information here
What are through hole components
Not suprisingly, these are components that go through a hole in a circuit board before being soldered.
The components you have used are through hole components
What are surface mount components
REMEMBER THIS SECTION IS ABOUT COMMERCIAL METHODS NOT WHAT YOU DID IN SCHOOL
Components that are mounted to the top or surface of the circuit board.
These are usually placed by a ‘pick and place’ machine onto a board that has already had solder applied before being soldered by passing the board through a ‘reflow oven’ that melts the solder and sticks down the components
Usually much smaller components that through hole and not done by hand.
What are the benefits and drawbacks to a manufacturer of using surface mount components?
Benefits
Speed - very high speed method once set up (which can take a lot of time)
Reliability - every circuit is of the same high quality
Size - circuits can be made much smaller meaning smaller products and possibly better sales
Less employees needed to manufacture circuits so reduced staffing costs
Drawbacks
Equipment is very expensive to purchase
Set up times can be very long - to program a new circuit for example could take days
Staff costs per person go up - staff are much better qualified and will be paid more
If being introduced, training will be required (which needs to be paid for)
Not suitable for one off or small numbers of circuits
What does ‘quality assurance’ mean in making PCBs?
REMEMBER THIS SECTION IS ABOUT COMMERCIAL METHODS NOT WHAT YOU DID IN SCHOOL
The planned activities that take place to make sure the circuits produced are fully functioning and high quality.
This is undertaken both DURING and AFTER manufacturing.
It could include obvious activities such as testing the final circuit but also includes ensuring the chemicals are at the right temperature and replaced regularly, randomly sampling the componenst to ensure they are high quality, making sure PCB board is used as it comes in as they do have a ‘shelf life’, testing continuity before adding components etc.
What is ‘automatic circuit testing’?
When you tested your circuits you tested for continuity of the tracks and the voltages at certain points in your finished circuit.
Commercially it would be far too slow for a person to do it, so there are automated machines that are programmed to test these things using very small probes that move from point to point. They will reject any circuits that fail.
In a full, mass produced company the circuits that come from soldering in the reflow oven are passed automatically to the testing machine with no people being involved.
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What is optical testing of circuits?
REMEMBER THIS SECTION IS ABOUT COMMERCIAL METHODS NOT WHAT YOU DID IN SCHOOL
This sounds like whay you did - “I looked at it and it seemed fine!”
Commercially though it is a far more developed and automated system.
A machine scans a circuit board and compares it with a scan of a range of ‘good’ circuits. Put simply, it is looking for differences between the circuit being tested and a good one.
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