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Picking the Correct IC Package

http://www.sparkfun.com/tutorial/Selecting-Package/ic-chart.jpg


ICs, or integrated circuits, can come in a number of different packages. Most are named as an acronym describing their layout based on shape, lead type, location, surface mount or through-hole. The earliest ICs came in a ceramic flat pack or compression circuit (see image below), a design that was a staple of military electronics for many years. From there integrated circuits moved on to DIP (dual in line) packages, which are what most people think of when they envision microchips, and further on to surface-mountable ICs. It’s important to always check the datasheet as sometimes properties and features differ between packages.

From http://www.decadecounter.com/vta/storepage.php?item=5&user=0
Early RCA Ceramic Flat Pack IC Courtesy of The Vintage Technology Association

What package will work best for you depends on a number of different variables, most importantly your application for the IC. For example, a hobbyist who is proficient in surface mount soldering might choose a TQFP package. This keeps the IC footprint small and easier to work with in terms of layout. In addition, this package keeps the profile of the board lower to allow it to fit into a thinner enclosure should the user need to enclose the board.

http://www.sparkfun.com/tutorial/Selecting-Package/ATMEGATQFP.jpg
ATMega328 in a TQFP Package

If a chip needs to be programmed on a separate board before being installed, a DIP package is easier to manage. Favored for their ability to be used in conjunction with a socket for easy switching of the ICs, DIPs are characterized as a rectangular package with thru-hole leads evenly spaced in parallel rows. The DIP package is also much easier to solder than the TQFP if a more permanent solution is needed, but the user lacks surface mount soldering skills. 

http://www.sparkfun.com/tutorial/Selecting-Package/atmega328_resize.JPG
ATMega328 in a DIP Package

The soldering methods to which you have access are also a key factor. Going back to the first example, a hobbyist would likely stay away from something in a BGA (ball grid array) package as this would prove harder to solder using techniques available to the average hobbyist. Ball grid array packages are usually reserved for more complex ICs and are favored for their low thermal resistance which allows for better heat dissipation. The ball leads on this package are an innovation from another package called a Pin Grid Array or PGA.

http://www.sparkfun.com/tutorial/Selecting-Package/BGA_resize.JPG
BGA or Ball Grid Array.  Image courtesy of Digikey

 


Sample Question: An advantage to using a surface mount IC is...

a) Solderability
b) Size
c) Interchangable
d) all of the above

Correct Answer: b, while more difficult to solder than most through hole components, most surface mount ICs allow you to fit a package with a lot of leads into a smaller, more low profile area.

Quiz Question - Digikey Part Numbers

Select the Digikey part number for a SOIC MAX232 IC.

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