AN2348 STMICROELECTRONICS | Alldatasheet

Document overview

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Technical content

Flip Chips. For information on 500 µm Flip Chips, see Application note AN1235. developed packages with reduced size, thickness and weight in the form of the Flip Chip. connections than the ones in standard plastic packages (such as TSSOP , SSOP or BGA). Figure 1. Typical Flip-Chip packages are available in mass production.

1 Product description

redistribution metal tracks to be minimized. compatible with the PCB design rules used for standard ICs. Optional coating on the flat side of the package is available. allows picking as in the standard SMD packages. on the flat side of the device.

2 Mechanical description

Mechanical dimensions of Flip Chips are provided through a product example in Figure 2. the connection requirements. Figure 2. Mechanical dimensions of a 5 x 5 bump matrix array (sample) .

through vertical focuses show a bump plus die coplanarity below 50 µm. detected by standard vision systems. Marking dimensions are linked to the die size. Figure 3. Flip Chip marking example for 5x5 bump matrix array.

3 Packing specifications and labeling description

section are in accordance with EIA-481-D, IEC 60286-3 and EIA 763 (783) standards.

3.1 Carrier tape

Figure 4. Standard tape width is 8 mm for die sizes smaller than 3 mm (dimension B0). Note: 12 mm carrier tape width may be used for a larger die size to be in line with EIA standards.

3.2 Cover tape

10E5 ohm/sq and 10E11 ohm/sq) polyester film cover tape with a heat activated adhesive. The cover tape tensile strength is higher than 10 N. between 165 and 180 degrees and the test is done at a speed of 120 ± 10% mm/minute. Table 1. Tape cavity sizing component rotation cannot exceed 10° max.

3.3 Reels

coming from 2 different wafer lots. the end of the reel and consists of empty, sealed cavities (see Figure 7). Figure 6. Seven-inch reel mechanical dimensions. Figure 7. Leader and trailer

3.4 Final packing

polyethylene bag (minimum of 4 mils material thickness). Reels are then packed in cardboard boxes. The complete description for packing is shown on Figure 8. Figure 8. Packing flow chart.

3.5 Labeling

shipped quantity and traceability references (Figure 9). history from the wafer fab to the customer’s location. Figure 9. Example of a reel label

Table 2. Parameter reel label

AN2348 Recommended storage, shipping instructions and descriptions Doc ID 12282 Rev 5 9/17

4 Recommended storage, shipping instructions and

Flip-Chip reels are packed under inert N2 atmosphere in a sealed bag. For shipment and handling, reels are packed in a cardboard box. STMicroelectronics thus recommends the following shipping and storage conditions:

  • relative humidity between 15% and 70%
  • temperature range from -55 °C to +150 °C Components in a non opened sealed bag can be stored 6 months after shipment. Components in tape and reel must be protected from exposure to direct sunlight. Moisture sensitivity level (MSL as per JEDEC J-STD-020C) is not applicable to Flip-Chip devices since there is no plastic encapsulation and so no risk of moisture absorption and related possible package cracks.

5 Soldering assembly recommendations

5.1 PCB design recommendation s for multi-bump Flip Chips

recommends the PCB design guidelines listed in Table 3.. Note: A too thick gold layer finishing on the PC B pad is not recommended (low joint reliability). size have to be properly designed (see Figure 10). Figure 10. Multi-bump Flip-Chip bump footprint the pads are connected to the lower layers using micro vias. Table 3. PCB design recommendations.

5.2 PCB design recommendati ons for 2-bar Flip Chips

recommends the PCB design recommendations listed in Table 4. recommended (low joint reliability). size have to be properly designed (see Figure 11). Figure 11. Solder mask opening Table 4. PCB design recommendations for solder bar pitch 400 µm

5.3 PCB assembly guidelines

stencil aperture of 330 x 330 µm2maximum and a typical stencil thickness of 125 µm. illustrated on the soldering reflow profile shown in Figure 12. Figure 12. ST ECOPACK reflow, specially above 150 °C. prevent any bump cracks, ultrasonic cleaning methods are not recommended. Table 5. ST ECOPACK

AN2348 Soldering assembly recommendations Doc ID 12282 Rev 5 13/17

5.4 Underfilling

Underfilling is not essential for Flip Chips. These devices can do without an underfill if the process temperature does not exceed 175 °C and if the process time is short (typically 5 minutes).

5.5 Manual rework

Flip Chips are able to tolerate one repair in addition to the two reflows mentioned in Section 5.3. As for other BGA type packages the use of laser systems is the most suitable form for Flip Chip repair. Manual hot gas soldering is acceptable but iron soldering is not recommended. For leaded Flip Chip manual rework the maximum temperature allowed is 260 °C (lead-free compatibility) and dwell time must not exceed 30 seconds. For lead-free Flip Chip manual rework, the maximum temperature allowed is 260 °C. The typical soldering profile of Figure 12 can be used.

5.5.1 Rework procedure

Rework process start with the removal of the device. To remove the device, heat must be applied to melt the solder joints so that the component can be lifted from the board. Large area bottom side preheaters may be used to raise the temperature of the board. This may help to minimize warping of the board, and minimize the amount of heat that must be applied on the component. Top heating may be applied to the component by using a laser or a convective hot gas nozzle. Nozzle size must be selected to match the component footprint appropriately. After top heating has melted the solder, vacuum is applied through the pick-up nozzle, and the component is lifted from the board. The heat should be carefully directed at the component to be removed to avoid adjacent components solder joints being reflowed. Shielding, control of gas flow from the nozzle, and accurate temperature control are the key parameters. Removing solder Next step is cleaning the solder from the work site. Due to space constraints and the need for accurate temperature control, automatic tools are recommended. Typically, site cleaners consist of controlled non-contact gas heating and vacuuming tools. The objective is to remove the residual solder from the site without damaging the pads, solder masks or adjacent components, and to prepare the site for application of new component.

  • Fully automated X,Y ,Z and theta control
  • Fully automated alignment using digital feature separation (DFS) technology
  • Precision force sensor and mass flow controller
  • Four zone bottom preheater
  • Flux dipping station
  • FireWire (IEEE 1394) controls
  • Visual machines software
  • Machine table including power supply cabinet ONYX32 Options
  • Dispensing head for solder paste, flux, underfill or adhesives
  • Non-contact temperature sensor
  • Site solder removal system

6 Changes

STMicroelectronics reserves the right to implement minor changes of geometry and manufacturing processes without prior notice. Such changes will not affect electrical characteristics of the die, the pad layout or the maximum die size. However for confirmed orders, no variation will be made without customer’s approval.

7 Quality

7.1 Electrical inspection

Products in Flip Chip are 100% electrically probed according to the critical parameters of the ST product specification. The last operation before packing is 100% electrical testing. The other parameters are guaranteed by technology, design rules and by continuous monitoring systems.

7.2 Visual inspection

A visual control is performed on all manufacturing lots according to the MIL-STD-883 method 2010.

8 Conclusion

applications where integration and performance are the main concerns of designers.

  • Remarkable board space saving (package size equal to die size and total height less than 605 µm)
  • Enhanced electrical performance (minimized parasitic inductance due to very short electrical paths and absence of redistribution layer)
  • High reliability due to integration of a whole function traditionally based on discrete interconnected components. Flip Chips are delivered in tape and reel and are fully compatible with other high volume SMD components (standard plastic packages or CSP/BGA packages) regarding existing pick and place equipment, standard solder reflow assembly equipment and standard PCB techniques.

9 Revision history

Table 6. Document revision history 15-Oct-2006 2 Added section 5.4.1 on Rework procedure. tape dimensions in Figure 4 and Figure 5. reflow profile in Figure 12. 19-Oct-2012 5 Corrected typographical error in Figure 12. Restructured Table 5.