ECE101 Section 5“Gadget Lab”

Lecture 3: Integrated Circuits and SolderingDr. Cindy Harnett

ECE Dept.

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.

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.

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)

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?)

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

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

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

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.

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

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.

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

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

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

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

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

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/

Teardowns

• Computer card• Electric toothbrush• CD player (Component identification)

• Have other teardowns for next time? (no TVs or computer monitors please)