CSPs: Hot new packages for cool portable products
10/01/1997
E. Jan Vardaman, Thomas Goodman, TechSearch International Inc., Austin, Texas
Until recently, fine-pitch leaded packages such as QFPs and TSOPs were the only packages available for high-density mounting in portable products. Ball grid arrays surfaced several years ago as an alternative to peripherally leaded packages. Within the past year, however, a new choice, chip-scale packages (CSPs), has emerged for applications requiring high-density packaging. The chip-scale package — sometimes called a chip-size package — is a small form factor package that is about the same size as the IC.
As many as 40 different CSPs are in various stages of development at some 30 organizations worldwide. Although no single CSP stands out as representative of these new packages, they can be divided into four categories — flex interposer, rigid substrate, lead frame, and wafer level (see table). Packages have either solder bumps, pads, or leads for interconnection to the printed circuit board (PCB).
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Today, CSPs are found primarily in products where portability demands small size and dense interconnect. Digital camcorders, flash memory cards, PC cards, cellular phones, and portable computers are just a few of the commercially available products containing CSPs. Sony's DCR-PC7 is well-known not only for being a passport-sized, fully functional digital camcorder, but also for containing 20 CSPs — four based on flex circuit material and 16 based on a laminate substrate. The packages from NEC and Texas Instruments (TI) Japan use wire bonding to connect the chip to the flex circuit, while Sony's own packages use flip chip technology to connect the IC to the laminate substrate. All 20 CSPs have solder balls on a 0.5-mm pitch for interconnection to the PCB. Sony was the first company to use CSPs in camcorders, but it is not the only one. Matsushita has introduced two digital camcorder models containing CSPs. The model NV-DE3 was introduced in February 1997, and the model NV-DS5 was introduced in May 1997. Both models take advantage of TI Japan's flex-based Micro Star BGA with a 0.8-mm solder ball pitch. With the competition heating up to produce the world's smallest, lightest, digital camcorder, product announcements of equipment using CSPs are expected to continue.
Flex-based and laminate-based packages are not the only CSPs found in today's small products. Cell Computing, a manufacturer of highly miniaturized electronics, continues production of its card PC with ceramic substrate CSPs supplied by Matsushita. Matsushita fabricates gold bumps on the IC using a modified gold ball bonder, then attaches the IC to the multilayer ceramic substrate using a conductive adhesive to create a small form factor package.
Notebook computers using CSPs have also been introduced. LG Semicon in Korea is supplying DRAMs in its bottom leaded plastic (BLP) package for use in a notebook computer. The BLP is a lead frame type package and can be used to replace a TSOP. The ability to provide a small package is the main reason for the use of the BLP in this application. Figure 1 provides a clear view of the size advantage obtained by using CSPs in a SODIMM.
Fujitsu is introducing an increasing number of products with a variety of CSPs. One cellular phone uses a bump chip carrier with 16 pins. Another cellular phone and a portable computer use the ultra small outline no lead (USON) package with 40 and 46 pins. Additional cellular phones and portable computers are planned that will use flash memory (48 pins) and microcontroller devices (168 pins) mounted in Fujitsu's fine pitch ball grid array. This fall, Fujitsu will introduce a new 72 MB flash memory card based on 36 USONs with 40 pins each.
 Figure 1. LG.Semicon's ultra small outline no lead (USON) package. SODIMM shown a) with TSOP and b) with bottom leaded plastic (BLP) package. |
In addition to supplying ASICs packaged in its own flex-based CSP, NEC also has plans to use the packages internally. A cellular phone will contain a DSP packaged in a flex-based CSP with 116 solder balls. Future personal digital assistants are being designed with CSPs.
The limiting factor in making products with CSPs is the availability of these small packages. For example, there is tremendous demand for Tessera's flex-based package, the µBGA, but the supply is limited. A long list of IC contract assembly houses and semiconductor suppliers have licensed the technology and are busy establishing high volume manufacturing lines. These companies include Amkor/Anam, Intel, Hitachi Ltd., Hitachi Cable, LG Semicon, Mitsui High-tec, Samsung, Shinko, SGS Thomson, and Texas Instruments. Supply problems for this package should improve by next year. Meanwhile, other companies such as Casio, Citizen Watch, and Fujitsu are offering to assemble die in the special CSPs they have developed. Many Taiwan-based contract assembly operations such as Advance Semiconductor Engineering, Orient Semiconductor Engineering, and Siliconware have plans to offer assembly services for CSPs.
Board-level assembly subcontractors are also preparing to offer their services for mounting a variety of CSPs on boards for many products. XeTel in Austin, TX, has developed a process for mounting Intel flash memory devices in µBGA CSPs on a test board. Six of these new packages can be mounted in the same area previously occupied by two TSOPs (Fig. 2). The packages, supplied in tape and reel, are mounted using a Fuji chip shooter at a speed of five packages/second.
 Figure 2. XeTel minicard with CSPs. |
The CSP is an emerging package with a bright future. In 1997, more than 40 million flex-based CSPs will be shipped, and this number is expected to grow dramatically as the use of these packages becomes widespread for flash memory. Because laminate-based packages are used for many ASIC and microcontroller applications and lead frame-based packages for memory, the numbers of these types of CSPs is also expected to increase. CSPs will remain the hot packages in cool portable products for many years to come.
Acknowledgment
MicroStar BGA is a trademark of Texas Instruments. µBGA is a registered trademark of Tessera.
E. Jan Vardaman is the president and founder of TechSearch International, providing licensing and consulting services in semiconductor packaging since 1987. Thomas Goodman is a senior technology analyst at TechSearch. TechSearch International Inc., 9430 Research Blvd., Bldg. 4 Suite 400, Austin, TX 78759; ph 512/343-4508, fax 512/343-4509.