Dealing with Obsolete Packages

Tekmos makes replacements for obsolete parts. While we can recreate any old design, our biggest obstacle comes in the packaging of the obsolete parts. In many cases, the packages themselves are obsolete. An example is the BQFP (Bumpered Quad Flat Pack), which was a high pin count package originally developed by AT&T and Intel, and which reached its peak volumes with the Intel 80386SX processor. Today, we are unaware of any vendor that offers this package. Another package that gives us problems are the PLCC packages. The 20 pin is unavailable, and the 28, 68, and 84 pins have very limited availability.

A simple solution is to have customers change their PCB to accommodate a new package. But this has problems. Frequently, the demand for older products is driven by regulatory demands. The same regulations that demand the continued use of obsolete parts also require the use of the original PCBs. Changing the board can require a new, expensive, and time consuming qualification. Remaking the original packages also poses problems.

Older plastic packages require mechanical tooling to form them into the correct shapes. The three main tools are the book mold, which forms the package, the de-junk tool, which removes extruded plastic from between the leads, and a shear and form tool, which cuts the leads from the lead frame, and bends them into the correct shape. These tools are expensive, costing roughly $100K each. An older package may also require a leadframe, which is generally purchased in 50K minimum quantities. Remaking the package can cost on the order of $350K up front, provided you can locate an assembler willing to do it.

Alternatives are needed, and Tekmos offers several. One option is the use of a LGA package. LGA stands for Landed Grid Array, and can be thought of as a BGA type package without the balls. It looks like a PCB with plastic on one side. The parts are formed in a block, and cut apart with a saw, so packages of any size can be made. Tekmos uses this approach to replace smaller PLCC packages. Because the LGA packages are quite thin, they have a maximum size of about 10 mm. Larger packages would tend to warp, and become difficult to attach to the customer’s board.

A second option is adapter cards. These come in two varieties. One option is to use a pattern on the bottom of the adapter that matches up with the original package footprint. We then attach our circuit to the top of the adapter. Our circuit must use a smaller package than the adapter, but this is not a problem with current packaging technology. This approach has a difficulty in that the connections are made under the adapter card, and are difficult to inspect.

Another option is to use an adapter card with castellated edges. Castellations are a series of plated through holes drilled around the edge of the adapter card. The adapter cards are cut apart directly through the holes, producing the castellated edge. This allows easy inspection of the solder joints. There is an economic disadvantage in that the Tekmos parts can only be attached after the adapter cards are cut apart. This increases the adapter card assembly costs.

Each case is different, and Tekmos can work with you to develop the best solution for your needs. Call us for more information.