BY RAY PURDOM, CLES TROXTELL AND EDGAR ZUNIGA
The advent of semiconductor materials being converted into electronic functions set off a revolution in electronic systems design. As electronic function decreased in size and cost, demand for it expanded rapidly. Today, billions of integrated circuits (ICs) are fabricated, assembled and shipped worldwide to support systems used in nearly every facet of everyday life. Board assembly has evolved to ultra-automated, high-speed, high-volume production lines. The packing methods and materials used to ship and distribute ICs must ensure that the component arrives at the pick-and-place point in an automated assembly line undamaged and in the correct position for pick-up. To this end, the industry has migrated to three basic configurations for shipping semiconductor ICs: magazines, trays and tape-and-reel.
Stick Magazine (Shipping Tubes) – Primary Component Container: Magazines are constructed of rigid clear or translucent polyvinylchloride (PVC) material and are extruded in applicable standard outlines that meet current industry standards. The magazine dimensions provide proper component location and orientation for industry-standard automated-assembly equipment. Magazines are packed and shipped in multiples of the single-magazine quantity. Multiple magazines are loaded into intermediate containers (bags and boxes) to form standard quantities for ease of handling and order simplification (Figure 1). Typical intermediate-level packing quantities for magazines vary by pin count and package type (Table 1).
Table 1. Example of magazine standard pack quantities.
Trays – Primary Component Container: Trays are constructed of carbon-powder or fiber materials that are selected based on the maximum temperature rating of the specific tray. Trays that are designed for use on components requiring exposure to high temperatures (moisture-sensitive components) have typical temperature ratings of 150°C or more. Trays are molded into rectangular standard outlines containing matrices of uniformly spaced pockets. The pocket cradles the component for protection during shipping and handling. The spacing provides exact component locations for standard industry automated assembly equipment used for pick- and-place in board-assembly processes. Trays are packed and shipped in multiples of the single-tray quantity, and then are stacked and bound together for rigidity. An empty cover tray is applied to the top of the loaded and stacked trays.
Table 2. Example of standard quantities for tray-packed ICs.
Typical tray stack configurations are five full trays and one cover tray (5+1) and 10 full trays and one cover tray (10+1). Customers may receive units in single or multiple stacks, depending on individual requirements. Components are arranged in the trays to match standard industry norms; standard orientation is to place pin 1 at the tray chamfered corner. Figure 2 is an example of a JEDEC tray outline with standard component orientation. Standard packing quantities vary by package size. Table 2 shows an example of TQFP style packages shipped in trays and their standard quantities.
Figure 1. Typical Stick magazine shipping tube.
Tape and Reel – Primary Component Container: Typical tape-and-reel configurations are designed to meet current industry standards. There are two generally accepted standards that cover the tape-and-reel packing configurations. EIA-481 applies to the embossed configurations, while EIA-468 applies to the radial-lead-device configurations. By far, the most popular configuration for active ICs is embossed tape.
Figure 2. JEDEC tray with properly arranged units.
Embossed Tape and Reel: Most active ICs are delivered in the embossed tape-and-reel configuration. This configuration consists of a carrier tape with a cover tape sealed to the carrier tape (Figure 3). This composite tape, loaded with components, is wound onto a reel. The reel is placed in a corrugated shipping box for transport and delivery. The three components of this packing configuration are the carrier tape, cover tape and reel.
Figure 3. Tape-and-reel packing (Ref. EIA-481).
Carrier Tape: Figure 4 shows the basic outline and dimension labels of the carrier tape. Typically, the carrier tape is constructed from a polystyrene (PS) or PS-laminate film. The unformed film thickness is 0.2 to 0.4 mm, depending on the size and weight of the component carried by the tape. Carrier tape design is defined primarily by component length, width and thickness. Component dimensions are the basis for the industry dimensional variables for carrier tape:
A 0 = Dimension designed to accommodate component width
B 0 = Dimension designed to accommodate component length
K 0 = Dimension designed to accommodate component thickness.
Figure 4. Carrier-tape dimensions (Ref. EIA-481)
For cavities with bottom pedestals, a K1 dimension is specified to identify the required pedestal height. W = Dimension defining overall width of the carrier tape. This must conform to accepted industry norms (8/12/16/24/32/44/56 mm).
Table 3. Examples of industry-standard quantities of ICs packed in tape-and-reel configuration.
P 1 = Dimension defining the pitch between successive cavity centers. This dimension must conform to industry norms (4-mm increments). Table 3 lists examples of the basic dimensions and standard quantities for some packages available in the tape-and-reel configuration.
Table 4. Moisture-sensitivity classification for SMT products.
Cover Tape: Typically, the cover tape is a PET film or film laminate, with adhesive applied to the underside of the film. Designs use either a heat-and-pressure adhesive or just pressure to ensure a positive consistent seal to the carrier tape. The film thickness, including adhesive, is 50 to 65 microns (Figure 3).
Table 5. Typical floor life for different package moisture-sensitivity levels.
Component Orientation: Component orientation in the carrier-tape pocket is governed by EIA-783, which states that orientation rules shall be followed sequentially until no other variation is possible:
- The largest axis of the component outline shall be perpendicular to the tape length (Figure 5).
- The edge of the package containing termination 1 shall be oriented toward the round sprocket holes (Figure 6).
- For the components where rule 1 and rule 2 do not establish a unique orientation, termination 1 shall be in quadrant 1 (Figure 7).
Table 6. Packing-material environmental coding.
Reels: The reels that contain the sealed carrier tape are constructed of polystyrene (PS) material. The reels can be constructed of one to three parts. Reels are shipped in various colors (blue, black, white or transparent), and they are typically recyclable (most suppliers participate in environmentally responsible recycling programs). Reel dimensions are governed by EIA-481 standards (Figure 8).
Plastic IC packages absorb moisture from the surrounding environment. This is a typical characteristic of the materials used in the construction of plastic packages (mold compound and die attach). The moisture inside the package increases or decreases to reach the relative humidity (RH) of the surrounding environment. Weight gain/loss analysis is used to determine the time that it takes for a package to reach moisture saturation or the time required for removing it. This information is used to specify maximum exposure times and minimum dry-baking times for a particular package.
Figure 5. Component orientation (EIA-783) rule 1.
Moisture inside the package turns into steam when the package is exposed to the vapor phase/infrared reflow and/or wave-soldering processes that are common in the fabrication of printed circuit boards (PCBs). The resulting steam and vapor pressure can cause cracking of the package – a phenomenon called popcorning.
Figure 6. Component orientation (EIA-783) rule 2.
Testing for Moisture Sensitivity: The sensitivity of a package to moisture-induced damage depends on many factors, including room temperature, RH and the construction of the package. Surface-mount packages are more susceptible to moisture-induced damage than their through-hole counterparts because surface-mount packages normally are exposed to higher solder temperatures. Through-hole parts are usually larger and, therefore, are stronger mechanically.
Figure 7. Component orientation (EIA-783) rule 3.
Most surface-mount products are tested for moisture sensitivity using the procedures outlined on EIA/JEDEC A112-A and EIA/JEDEC A113-B. JEDEC levels one through six define relative levels of moisture sensitivity. Level one denotes a package that is not moisture sensitive. Any package denoted level two or higher requires removal of moisture by baking or under vacuum, followed by dry packing to protect it during shipment. Shipping containers are labeled according to the product moisture-sensitivity classification.
Most IC manufacturers' packages have been tested and classified according to their sensitivity to moisture-induced damage. An example of typical classification of surface-mount-technology (SMT) packages is listed in Table 4.
Figure 8. Typical reel outline as defined by EIA-481.
Dry Packing: Dry packing consists of baking the packages to reduce moisture to a level not to exceed 0.05 percent by weight. Then, the units are placed in a moisture-barrier bag, along with desiccant, to keep the moisture inside the bag to a level <10 percent RH. Each product is labeled as moisture-sensitive, outlining the necessary precautions for handling the product. Table 5 shows the typical floor life for the different package moisture-sensitivity levels.
The typical packing method requires the following materials:
- Magazines (plastic tubes), trays, tape-and-reel
- Moisture-barrier bag
- Labels (moisture-sensitive identification [MSID] label, dry-pack caution label)
- Humidity-indicator card.
Moisture-Sensitivity Labeling: Primary and intermediate containers for moisture-sensitive packages are labeled with standard moisture labels, as defined in current JEDEC standards. The MSID label is applied to the outside of the intermediate container, typically near the barcode label, to indicate that moisture sensitive packages are inside. The moisture-sensitivity caution label is typically applied to the outside of the sealed moisture-barrier bag; this label contains detailed information specific to the device (moisture-sensitivity level, floor life, etc.). The humidity-indicator card is placed inside the sealed moisture-barrier bag and can verify that the product has been stored and shipped in a low-humidity environment.
Environmental: The IC industry strives to optimize the packing density of each configuration to minimize the volume of packing material entering the industrial waste stream. Where possible, pure materials, such as PS/PVC, are used to ease disposal. Cellulose material suppliers are encouraged to incorporate recycled material to reduce their consumption of virgin material. Typical packing materials used and their respective recycling code assignments are listed in Table 6.
The authors would like to thank Beverly Houghton for helping with the images and standard quantity tables, and Randy Kirk for assisting with the standard packing samples.
- EIA-481 Standards, excerpts used to assure complete alignment.
- EIA-783 Component Orientation.
- JEDEC Moisture Sensitivity Testing Procedures: EIA/JEDEC A112-A, EIA/JEDEC A113-B.
RAY PURDOM, standard linear and logic packaging drafter, CLES TROXTELL, materials and process engineer, and EDGAR ZUNIGA, standard linear and logic packaging manager, can be contacted at Texas Instruments Inc. For more information, contact Edgar Zuniga at P.O. Box 84, m-s 812, Sherman, TX 75091-0084; 903-868-5820; E-mail: [email protected].