• Access to IC chips is limited.microelectronics and chips image by Albert Lozano from Fotolia.com
  
  Integrated Circuits (IC) are central to most modern electronic devices. It is because of ICs that the computers we carry in our pockets (as part of our phones) are more powerful than the early computers that took up several rooms. ICs do, however, have some disadvantages. It is impossible to stick a probe or attach a wire to the center of an IC -- the only access to the IC is through a few pins.
  
  

DIP Chips

• Most chips are Dual In-line Package (DIP) chips -- plastic rectangles with a row of pins along the two long sides. This works pretty good as long as you need only a few connections for input to and output from the chip. It does have the disadvantage that both input and output ports must be located near the sides of the Integrated Circuit (IC). If this is impossible, the inputs (or outputs) will require long wires which add impedance to the circuits. As circuits have gotten larger -- there are now entire processors on a single chip -- it has become necessary to have more pins. The increased number of pins require that they be too close together and have made the DIP style chip impractical. Ball grid arrays were designed to overcome the problems in the DIP chips.
  
  

Pin Grid Arrays

• The first solution to the problems imposed by the large number of pins need by larger chips is the pin grid array. These large packages have an array of pins underneath the package. This not only provides more pins, it solves the problem of requiring that the inputs and outputs go the the sides of the IC only -- or require extra long internal wires. As the pins are located all over the IC the connections can be more direct. Pin grid arrays introduced another problem. When plugged in, the pins are hidden and impossible to probe. This is mostly a problem when you want to make sure that all the pins are making a good contact -- or you need to probe a pin as part of a test to see how the IC chip is preforming. Temperature and vibration can cause a problem with some of the pins in the array -- and this is exactly the problem that led to the development of the ball grid array.
  
  

Ball Grid Arrays

• Ball Grid Arrays are exactly like pin grid arrays except that there is a ball of solder in the place of each pin. The platform is an array of sockets that the balls fit into. At instillation time the platform is heated and the ball grid array is firmly pressed into place. If done correctly. the ball grid array is securely attached to the platform. A securely attached ball grid array solves all the problems inherent in both DIP chips and pin grid arrays.