Bottom termination standard nears completion

Array packaging has seen widespread usage over the past decade, but many chipmakers have been looking for packages that have lower costs than ball grid arrays. Those cost pressures drove the development of a number of different packages that cut costs by eliminating the solder balls, putting chips on wire frames that connect to circuit boards.

This class of products, generally called bottom termination components (BTC), has many proponents. Chipmakers like BTC because it’s inexpensive, while electronic engineers like this package style because the distances signals have to travel are short and there’s usually a good thermal connection because the parts touch the board. BTC components are economical  to make, so they’re in widespread use, typically in plastic packages with 100 leads or fewer.

“This is the package of the future because it reduces cost,” said Dieter Bergman, IPC’s director of technical transfer. The BTC category includes a range of components including QFN (quad flat no lead) DFN (dual flat no lead), SON (small outline no lead), LGA (land grid array) and MLF (micro lead frame).

While chipmakers like the low cost, the small leads on the bottom of these parts pose many challenges for assemblers. Their needs are being addressed by the development of IPC-7093, a standard that provides guidelines and best practices for producing circuit boards that use the parts.

The challenge that manufacturing engineers often face stems from their use of metalized terminations integrated into the bottom of the package. These leads are more difficult to work with than the leads and solder balls of other similar components.

“The problem is that everything has to be perfect,” said Ray Prasad, co-chair of the IPC 5-21h Bottom Termination Components task group. “You can’t have too much solder or the parts will float.”

Another challenge is that the laminate substrates of the end system must be extremely flat so the solder bonds under the BTC package can form good electrical and mechanical bonds. These challenges sparked much interest in IPC-7093, since both chipmakers and board assemblers will benefit by combining reliability and simple, inexpensive packaging.

Many of the parts go into inexpensive products that are effectively throw aways, but some are used in demanding applications like automotive powertrains. That makes reliability a necessity.

IPC stepped in to write guidelines after many manufacturers complained about problems with the quality of finished boards.

“These parts have no forgiveness. Manufacturing processes are much more critical than what you have with BGAs, which are far more forgiving,” said Prasad, who’s also head of the Ray Prasad Consultancy Group.

The need for a standard is evident in the many approaches that have risen as assemblers responded to the challenges that arose when they dealt with a range of package styles.

“Assemblers have developed different solutions,” Bergman said. “Some do checkerboards of solder and drill holes so the heat can go down to ground planes that dissipate heat.”

Pulling the best of all these solutions together is a key benefit that comes when companies share data and discuss the pros and cons of different solutions they’ve tried.

During IPC APEX EXPO, committee members voted to accept the document pending minor revisions and final editing. Committee members predict that the specification will be published in the September.

2 Comments

  1. Posted July 28, 2010 at 9:55 pm | Permalink

    It’s amazing how much/many IC/chip components are in cars today. I still think there is a risk and possible bottleneck with the substrate manufacturers; there are only a handful in the world. If something bad happened to one or two of them it would affect the global supply.

  2. ozzie johns
    Posted March 24, 2011 at 1:08 pm | Permalink

    IPC standard time for puller parts


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