Ball grid array (BGA) and many other high density packages have been utilized by electronics manufacturers by directly attaching the devices to printed circuit boards (PCBs). As semiconductor technology rapidly advances making more frequent package upgrades and interchangeability more prevalent, direct soldering of the BGA devices may no longer be feasible requiring an alternative solution for test and production applications. One possible solution is the use of BGA sockets.

Currently there are two primary types of BGA sockets available on the market- one-piece and two-piece construction. Both types serve as the interconnection between the device component and the PCB and both have their advantages and disadvantages depending on the application.

The two piece construction BGA socket system (Figure 4-1) includes a socket with the same footprint as the BGA device and has an adapter with the same footprint as the upper solder pads in order to receive BGA devices. For the two-piece construction to work properly, the BGA must be soldered to an adapter that is inserted into a socket. The socket is then assembled on the PCB. The one-piece construction socket does not require a soldering process to attach the BGA device to the socket and thus eliminates the extra assembly step. The primary advantage of the two-piece socket construction is its up-front lower acquisition cost.

The one-piece BGA socket (Figure 4-2), designed for testing BGAs without soldering, functions through the mechanical contact forces. The connection mechanism utilizes the compression force applied on the BGA to 1) create enough contact normal force and 2) minimize the contact resistance. A close examination of the one-piece socket reveals that mechanical forces on each contact are kept constant by spring force actions, which are provided either by pogo pins, spring interposers, or other design features. The sockets with solder tails or solder balls are reflowed onto the PCBs to make the connections. The BGA is then inserted into some type of guiding feature to align the BGA to the contact pins. Finally a selected heat-sink is screwed into the top of the BGA to make the connections between the BGA solder balls and the socket pin. Most of the socket body is made from high temperature thermoplastic or FR-4 materials. Depending on the pin design, the socket may also be used for test land grid arrays (LGA's).

The advantages of using one piece BGA sockets are 1) they allow for the interchangeability and retesting of BGA devices, and 2) they eliminate the need to solder the BGA device to the socket. The major disadvantage is that they cost more than the two-piece construction. Because the function of the one-piece sockets is dependent upon the uniformity of compression force distribution, spring force consistency, contact resistance level, and the dimensions of the socket, these factors must be taken into consideration when making design choices in addition to the common decision factors of performance, operating temperature range, size and cost.

It is highly recommended that the designer or component engineer request reliability test results (which may not be published on the data sheets) from the vendor. Several manufacturers such as Advanced Interconnections, Aries Electronics, Emulation Technology, Ironwood Electronics and Wells-CTI are offering the one-piece sockets in a wide range of quantities.