BGA ...Who ever would have thought?
10/01/2000
By Mark Dorio
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BGAs, BGAs, BGAs everywhere! How many different types of BGAs are there? There are BGAs that use ceramic substrates, organic substrates, flex tape substrates, thin film substrates and metal (leadframe) substrates. There are BGAs with solder ball pitches at 1.27 mm, 1.0 mm, 0.8 mm and 0.5 mm (with a few other pitches in between). There are BGAs that are wire bonded and there are BGAs that are flip chip. There are over-molded BGAs and there are BGAs that are liquid encapsulated. There are thermally enhanced BGAs. There are cavity-up and cavity-down BGAs. And there are BGAs with multiple chips inside. There are BGAs with as few I/Os as four and as many as 3,000. Did I overlook some BGAs? Probably, as there are new versions emerging every day. I'm having trouble keeping up (and I bet you are, too!). The point is that the BGA is a package that continues to grow significantly in volume, is relatively easy to manufacture in a variety of formats, is easy to handle, has a good average selling price, and continues to become more widely accepted and embraced. In general, it is a 'package for all seasons.'
Breaking Out the BGA
Back in the early to mid-1990s, I tried to convince my management board to make a significant investment and effort in BGA technology to take a leadership position and to help set standards for manufacture. I wasn't successful; the management board at that time opted to allocate resources (both financial and human) to lead-on-chip applications, which they believed to possess more opportunity for the company. Now I suppose that either I didn't argue my case adequately or they just couldn't understand the advantages that the BGA package type would present. Or perhaps they couldn't understand the dynamics (and volatility) of DRAM packaging versus the more predictable microprocessor, FPLD, ASIC packaging applications. Or maybe there was a little of that NIH syndrome in effect (see my September column).
Of course, hindsight is 20/20. And it is nice to say, "I told you so." But the truth of the matter is that, to most advanced packaging engineers, the BGA held great promise since its inception, and time has shown it to be more successful than first imagined. The BGA is a package type that offers a myriad of increased performance benefits and has extreme application in advanced packaging of the semiconductor.
The true need for increased packaging performance has risen out of the need for continuous improvement in device speed and density. As silicon chip performance increases (it is not uncommon for clock rates to exceed 1GHz today), so does the need to develop packaging technologies that do not diminish this performance level. It becomes increasingly necessary to use package types that reduce signal attenuation and can increase I/O density and device functionality. Because a leadframe-based package structure, such as a QFP package, has only the capability of performing at frequency levels of 250 MHz (requiring significant impedance matching even at this frequency), it quickly becomes apparent why the BGA is becoming more popular. The BGA package design has the increased ability to route data, set a ground plane, form doublets or triplets of data streams, and reconnect data from one sector of the chip to another (so as to avoid the inherent limitations in the aluminum metal layers largely in vogue at this time).
Technical Advantages
As the BGA package performance has technical advantages over other types of packages, it is necessary to fully understand these advantages and be able to position them into the appropriate application. Because of this, packaging engineers' technical skillsets for the BGA package differ. Packaging engineers need to be deeply involved in BGA packaging to:
- Understand electrical performance between the silicon and the package
- Understand how to lay out the BGA substrate to optimize silicon performance
- Understand the various materials and material options being used (or which are available) to obtain the desired device performance and reliability levels.
It is necessary for BGA packaging engineers to be true packaging designers, with designs that are able to contribute or enhance the performance of the silicon. It is not sufficient just to know how to build a BGA - engineers must know how to design BGAs to meet customers' requirements.
What's That You Say?
Some may protest that BGA packages reflect less than 10 percent of the total packaging market (units) and that the BGA forecast for the year 2004 is only for about 6 billion units. So why all the fuss? Well, many of the leading IC microprocessor, FPLD, ASIC houses - the real drivers of the business - have issued business edicts stating that new package designs will be in BGA format. So just maybe the forecasts are a little conservative.
Will the BGA become the highest volume runner? No, definitely not. But the BGA, being the package that can provide the highest degree and variation of performance capabilities, can provide some very attractive margins. This is, of course, if a company understands how to design and use those capabilities and apply them to its customers' needs better than the competition. The financial rewards will be very attractive if engineers understand how to seize the moment and have the appropriate technical acumen to do so.
In summary, the BGA is truly an excellent package - better than most could have predicted. And in this vein, I would like to tip my hat to the packaging pioneers who have engineered the technical details and fostered the infrastructure to make this package a success, to the engineers who had the technical understanding of what the package is capable of providing and the predictable vision of the applications it could be used in - truly, advanced packaging at its best!
MARK DiORIO, chief executive officer, can be contacted at MTBSolutions Inc., 1630 Oakland Road, Suite A102, San Jose, CA, 95131-2450; Tel. 408-441-2173; Fax: 408-441-9700; E-mail: [email protected].