ece101 section 5 “gadget lab” lecture 3: integrated circuits and soldering dr. cindy harnett ece...
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ECE101 Section 5“Gadget Lab”
Lecture 3: Integrated Circuits and SolderingDr. Cindy Harnett
ECE Dept.
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What is an “IC” ?
• Integrated circuit--more than a single resistor, capacitor, or transistor. Several components are integrated into one buglike package.
• Can have any function--see the datasheet
• Denoted by “U” on a circuit board (U1, U2, etc) for some reason.
• Thousands of kinds are available: amplifiers, “AND” gates, other logic gates, counters, microcontrollers and computer chips are ICs.
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Silicon chemistry enables microscopic circuit production
• Silicon can be formulated with a small fraction of phosphorus, boron or other ions. Small amounts: semiconductor (transistor). Large amounts: metallic (a wire or resistor)
• Silicon in an oxygen atmosphere forms an oxide (glass). Highly insulating (the filling in a capacitor)
• Layer by layer, tiny patterns of insulators, semiconductors and metals are arranged on silicon to form an integrated circuit.
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Transistor built at U of L shows IC construction.
• Pass around: Microcircuit on silicon made in the Belknap cleanroom
• A wirebonder is used to bring connections to the outside world
• Clear epoxy covers the circuit and protects the wires
• Industry uses black epoxy (many circuits are light-sensitive and/or proprietary)
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IC Sourcing
• On the Digi-Key website, why are there 269 choices for the 555 timer IC?
• Dual and single versions
• Different packages• Different current
ratings• Different sales
volume (buy 1 or 3000?)
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Deciphering Datasheets• Online catalogs nearly always
link to datasheets. Example: the 555 timer IC. (Muscle Wire, Firefly, and Theremin projects)
• Crucial items: absolute maximum voltage rating, power requirements, pinouts.
• Near the beginning, a paragraph or more on the circuit’s application and possibly example circuits
• Lots of graphs showing circuit parameters
• Finally, “mechanical data” showing size and shape of different versions the IC
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IC Safety• ICs generally have more to worry
about than you do. However, the ones we use are pretty robust.
• Electrostatic discharge (ESD) can short out devices by putting a different voltage on parts a few microns apart (Electric field: “volts per meter”)
• ESD can be prevented, especially grounding your fingertips by touching the table or chip container before touching chips.
• Also, as a general rule, apply power to a chip before applying input/output
signals.
ESD-damaged IC photo at http://www.bunniestudios.com/blog/?cat=6
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Breadboarding a 555 Timer• We’ll use a 555 timer IC to make
a LED flash at ~1Hz.• 2 resistors and a capacitor
determine the timing of a pulse train from the 555:
• Frequency=1.44/((R1+2*R2)* C)
http://www.markallen.com/teaching/ucsd/147a/lectures/lecture4/5.php
Maximum values for R1 and R2: 3,300,000 ohms (3.3 meg ohms)Minimum values for R1 and R2: 1,000 ohmsMinimum recommended capacitance: 500 pFMaximum capacitance: Limited by capacitor leakageMaximum frequency: Theoretically 1 MHz, but in practical usage, around 300 KHz
The fine print
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Breadboarding a 555 Timer IC• Pin 1 to Ground.
• Pins 4 and 8 to 6V.
• Pins 2 and 6 connected together.
• R1 between pins 7 and 8 (1000 Ohm: brown, black, red, gold)
• R2 between pins 6 and 7 (4700 Ohm: yellow, purple, red, gold)
•C between pin 2 and Gnd: 100 microFarads- put minus side at gnd!
•LED from Pin 3, thru 220 ohm resistor (red, red, brn, gold), to gnd.
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Soldering• Heat the part, then solder will flow onto it• A small bit of solder on the tip of the iron
will help make thermal contact• Datasheets show max temperature--you
can eventually damage an IC by heating too much
• Excess solder is removed by copper braid “wick” or vacuumed by “solder sucker”
• Solder contains a flux core that helps prep the metal surface to accept solder. Extra flux can be dispensed from pens/bottles.
• Copper, platinum, gold easy to solder with mild flux; stainless steel needs stronger flux
Heat the wire and the copper pad,then apply the solder
Wire
Solder
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Use sockets when you don’t want permanent attachment
• DIP sockets add a “solderless breadboard” plug-in style attachment for your 555 or similar chip.
• Good for microcontrollers that have to be reprogrammed or reused.
• ZIF sockets (Zero Insertion Force) also good for such chips. Available for surface mount chips. A reversible clamp or lever moves clips into contact with the pins. Can be expensive.
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How do I get a custom PCB?• Printed circuit boards (PCBs)
can be produced on a thin film of copper on an insulating base.
• Phototransfer and etching of your design is done by PCB companies (ExpressPCB)
• People on campus use a cutter to machine the copper, for simple boards
• Wax printing and copper etching process is also done locally
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Freeform soldering
• No printed circuit board, just parts• Not typically used in industry.• Needed for Solar Robot project
and (to a smaller extent) the solar charger project.
• Take “thermal mass” into account: wires and thin film solar cells heat quickly, but motor takes a long time in contact with the iron
• Need some practice holding onto components
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Advanced soldering: surface mount parts with small spacing
• Surface mount devices (SMDs) are often the next step to miniaturize your design.
• A fine-tipped soldering iron works on SOIC parts with ~1mm spacing (Electroluminescent project)
• Attach finer-pitched parts (typical QFP parts have 40 pins and up, 0.5 mm or less apart) by stenciling solder paste, attaching part and sending all through a “reflow oven”
• Also BGA parts (Ball Grid Array) with all pins under part. A soldering iron would not work here.
• Remove mistakes using ChipQuik low melting solder.
Solder paste being applied to 132 pads
Surface tension pulls part into place during heatinghttp://www.seattlerobotics.org/encoder/200006/oven_art.htm
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Industrial board assembly• For larger quantities,
boards can be sent out to be “stuffed” with components.
• Smaller and smaller production runs are possible.
• Companies use “pick and place” machines along with components in “tape” form to speed the process.
http://www.brightmanufacturing.com/ShopPhotos.htm
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Free your circuit from the solderless
breadboard• Use a “generic” printed circuit
board to duplicate the connections on the solderless breadboard.
• Use “Helping Hands” (not Yelping Hands) to solder
• Wear safety glasses• Where’s the fire extinguisher?
Soldered connectionsare on the back
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Component identification
• Some websites help you learn to identify ICs and other components (links on BlackBoard)
• Good for identifying a “mystery component” from a salvaged board or a junk drawer.
• Teardowns- new insights??http://www.uchobby.com/index.php/2007/07/15/identifying-electronic-components/
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Teardowns
• Computer card
• Electric toothbrush
• CD player (Component identification)
• Have other teardowns for next time? (no TVs or computer monitors please)