All the WLPs, CSPs and even SiP will negate attempts at $20 phones.

With more than a billion units expected to ship in 2007, the mobile phone has become the volume driver both for IC package shipments and new packaging technology developments.

Today’s cellphones contain a variety of packages: WLPs; CSPs with laminate substrates (and even a few with flex circuit or ceramic substrates), and leadframe-based CSPs such as QFN or SON packages. Almost all phones contain stacked die, and an increasing number contain stacked packages called package-on-package (PoP), especially with the inclusion of logic devices. With more packages containing logic and memory, growth for what the industry terms system-in-package (SiP) is exploding.

Many of the packages have small body sizes and low I/Os compared to packages found in PCs or game machines. Typically, the CSP outer lead pitch is 0.5 mm, but an increasing number of 0.4 mm packages are in production, and some companies are planning for 0.3 mm pitch packages.

Wafer-level packages. The most famous phone containing WLPs remains Motorola’s RAZR phone, with at least 14 wafer-level packages.1 While the ultra thin phone was reported to be the fastest-selling in history (more than 50 million units in a two-year period), it failed to generate profits because of discounting – perhaps a bit too much (no fault of the technology).² Almost every cellphone shipped today contains a WLP. Nokia’s 6131 phone contains at least a dozen. Cellphone models from many other companies also contain WLPs, including Fujitsu, Panasonic, NEC, Mitsubishi, Sharp and others. Typically, wafer-level packaging has been used for small die with low I/Os, but this is changing. Today’s die size ranges from 1.4 x 0.9 mm to 5.5 x 5. 5 mm, with as many as 120 I/Os. The WLP thickness ranges from 0.27 to 0.75 mm, one reason they are used, as cellphones trend toward thinner products. Nokia has recently announced a thin folding model that will be a little less than 0.75" thick.³

CSPs. A variety of CSPs are found in today’s cellphones. Most use a laminate substrate, but there are examples with laminate and tape substrates. One of the high pin count parts with 289 I/Os uses a tape substrate and has a body size of 12 x 12 mm. The thickness is just 1.2 mm and the I/O pitch is 0.5 mm. Many leadframe-based CSPs are also used.

Stacked die packages have been common for many years, with as many as five die found in production today. While the two die stacks are very common, die stacks with many more are increasingly common. Stacks containing as many as five die are in production. With continuing demand for packages with a height of less than 1.4 mm (1.2 mm or 1.0 is optimal), die must be thinned. Stacked die packages of 75 µm die thickness are in high volume production today, and 65 to 70 µm is qualified and moving into production at companies such as STATSChipPAC. Production of 50 and even 40 µm die thickness may see production in 2008. While many companies use the dicing before grinding process to dice thin wafers, new dicing techniques are being adopted, including laser and plasma.

An increasing number of phones from companies including Motorola and Nokia will use PoP. While the PoP is thicker than a stacked die CSP, thin PoP versions have been introduced using a cavity in the substrate. This makes possible 1.4 mm package thickness; a cavity in both packages achieves 1.2 mm package thickness.

Package selection is driven by the different needs in each phone model. In some cases there are more WLPs, and in others stacked die packages. Sometimes there are more QFNs or laminate-substrate CSPs. PoP (done at the board level assembly) is the choice for many companies when logic and memory need to be packaged together in a z-direction. Sometimes, a package-in-package (PiP), where two individual packages are overmolded together, is the choice when a company needs a package with a smaller footprint or greater electrical performance. No one package meets all needs, and a mixture of packages can be found on today’s phone boards. This trend is expected to continue.

‘A’ is for …

Everyone is talking about Apple’s new cellphone, scheduled to start shipping mid year with a price tag of around $500 (Figure 1). While its name – iPhone – is being contested, (why not just call it the Apple phone?), there is no question that the product has caught the imagination of many. The phone will be packed: quad band, a large touchscreen, 2 MP cameras, Bluetooth, WiFi, and 4 or 8 GB of memory. Component suppliers include Marvell (WiFi), Samsung (applications/video processor), Infineon (baseband processor), Broadcom (touch screen controller), CSR (Bluetooth), and Altus (camera module). Few details on the phone are available, and even fewer about the semiconductor packages. One can expect to see highly integrated packaging including SiPs.


Twenty-dollar phones? Is this a possibility? Texas Instruments is reported to be developing ICs for low-cost ($20 to $35) mobile phones aimed at developing countries.⁴ The cost of the silicon alone would more than exceed the $20 price tag, so a subsidy is in the equation. While a $20 phone is a nice target, most of the phone OEMs’ business models would not sustain such a product. Instead, look for increased functionality, increased complexity and greater integration, and higher-end mobile phones for the consumer of tomorrow. Oh yes, and make that a thin phone, please.

References

1. E. Jan Vardaman, Circuits Assembly, November 2006, p. 16.

2. The Wall Street Journal, Jan. 6, 2007, p. A1.

3. The Wall Street Journal, Jan. 8, 2007, p. A3.

4. InfoWorld Daily, Jan. 17, 2007.

E. Jan Vardaman is president of TechSearch International (techsearchinc.com); jan@techsearchinc.com. Her column appears bimonthly.

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