SMART Group BGA Solution- A Cost Effective Solution to Dummy Components

by Bob Willis SMART Group

Ball Grid Array (BGA) is becoming a widely used technology in a vast range of products including consumer, telecommunications and office based systems. As an area array device it provides high packing density with a relatively easy introduction cycle. The bulk of applications using BGA are telecommunications, office computer and consumer products which means that it is for volume applications. 

With any new technology it is inevitable that engineers must consider production trials on assembly, rework and inspection. This is necessary to define process parameters, demonstrate capability to customers and allow the  training of production staff with theses new devices. Often parts are necessary for equipment trials if new machines are required for product introduction. One of the major issues is the cost of fully functional or dummy BGA components for these very necessary projects. Parts can range in price from £15-35 each.

Having faced the same financial problems in the past when setting up production lines and practical demonstrations at exhibitions a solution needed to be found. So why not just make your own devices for a few pounds using existing manufacturing facilities. It should be bore in mind that a number of BGA manufacturers effectively do this on there products.

The SMART Group demonstration BGA figure 1 have been used successful in production for the last few years. They are an ideal solution to the problem on component availability. Quite simply they are just 1.6mm FR4 laminate circuits with 63% tin 37% lead solder terminations formed by screen printing paste and reflow. First a circuit panel approximately 200mm x 400mm is produced on double sided copper laminate. A multiple pattern of 361 0.025" round pads are etched on to one side of the panel with a company logo on the alternative side. Obviously if different pin out devices are required they can be produced in the same way. Remember if you are already laying out a new design you have the necessary pattern. The panels after etching are coated with solder resist and imaged to expose the round copper pads.

The final fabrication operation is "V" scoring the panel to allow each of the parts to be removed at a latter stage. The scoring operation defines the BGA size. The exposed copper pads are treated with an OSP coating to preserve the solderability. The OSP is used as this is the simplest process.

To form the terminations panels are printed with solder paste with a stencil on a conventional printer before reflowing the panels. The solder paste apertures are 0.030" etched in a 0.010-0.012" stencil. Increasing the stencil thickness can be done but the amount of paste defined in such a small area tends to make the stencil stick to the board and lift it at the end of the printing operation. During the reflow operation the solder paste reflows, wets the pads and due to surface tension the solder paste forms a ball like termination. Ideally this is conducted in a nitrogen environment to preserve the surface of the ball terminations. The use of nitrogen also provides a more ball like appearance.

Depending on the solder paste activity used the panels may be cleaned at this stage. A key factor of the paste is that it must not slump during reflow as it will cause multiple shorts if it does. The yield in terms of BGA devices from this manufacturing technique will be between 80-85%.

It is difficult to achieve the same volume of solder in the balls using this method but for all practical purposes this is not so important. When the panels are broken up there are hundreds of parts available for production trials. Using this technique guarantees that plenty of the components are available for production trials and more importantly for operator training. Often due to the cost of normal parts there just sent enough parts for operators to gain experience before working on real products.

Bob Willis is an independent process consultant. Further process advice  and information is available on Bob Willis Internet Home Page:http://www.bobwillis.co.uk or contact him on  Email: EPS@bobwillis.co.uk