SPRAA99C March   2008  – May 2021 AM3351 , AM3352 , AM3354 , AM3356 , AM3357 , AM3358 , AM3359 , AM4372 , AM4376 , AM4377 , AM4378 , AM4379 , OMAPL138B-EP , TMUX646

 

  1.   Trademarks
  2. 1Introduction
  3. 2PCB Design Considerations
    1. 2.1 Solder Land Areas
    2. 2.2 Conductor Width/Spacing
    3. 2.3 High-Density Routing Techniques
    4. 2.4 Via Density
    5. 2.5 Conventional PCB Design
    6. 2.6 Advanced Design Methods
  4. 3Reliability
    1. 3.1 Reliability Calculations
    2. 3.2 Package Characteristics
    3. 3.3 Thermal Modeling
  5. 4Surface-Mounting nFBGA Packages
    1. 4.1 Design for Manufacturability (DFM)
    2. 4.2 Solder Paste
    3. 4.3 Solder Ball Collapse
    4. 4.4 Reflow
    5. 4.5 Inspection
  6. 5Packing and Shipping
    1. 5.1 Tray Packing Method
    2. 5.2 Tape-and-Reel Packing Method
    3. 5.3 Tape Format
    4. 5.4 Device Insertion
    5. 5.5 Packaging Method
  7. 6Sockets
    1. 6.1 The Design Challenge
    2. 6.2 Contacting the Ball
    3. 6.3 Pinch Contact
    4. 6.4 Micro Tuning Fork Contact
    5. 6.5 Texas Instruments Sockets
  8. 7Summary
  9.   A Frequently Asked Questions
    1.     A.1 Package Questions
    2.     A.2 Assembly Questions
    3.     A.3 Small Body nFBGA Package Questions
  10.   B Package Data Sheets
  11.   C Thermal Modeling Results
  12.   Revision History

A.2 Assembly Questions

Q What alignment accuracy is possible?
A Alignment accuracy for the nFBGA package is dependent upon board-level pad tolerance, placement accuracy, and solder ball position tolerance. Nominal ball position tolerances are specified at ±50 μm. These packages are self-aligning during solder reflow, so final alignment accuracy may be better than placement accuracy.
Q Can the solder joints be inspected after reflow?
A Process yields of 5-ppm (parts per million) rejects are typically seen, so no final in-line inspection is required. Some customers are achieving satisfactory results during process set-up with lamographic X-ray techniques.
Q How do the board assembly yields of nFBGAs compare to QFPs?
A Many customers are initially concerned about assembly yields. However, once they had nFBGA packages in production, most of them report improved process yields compared to QFPs. This is due to the elimination of bent and misoriented leads, and the ability of these packages to self-align during reflow. The collapsing solder balls also mean that the coplanarity is improved over leaded components.
Q Are there specific recommendations for SMT processing?
A Texas Instruments recommends alignment with the solder balls for the CSP package, although it is possible to use the package outline for alignment. Most customers have found they do not need to change their reflow profile.
Q Can the boards be repaired?
A Yes, there are rework and repair tools and profiles available. TI strongly recommends that removed packages be discarded.
Q What size land diameter for these packages should I design on my board?
A Land size is the key to board-level reliability, and Texas Instruments strongly recommends following the design rules included in this document.
Q The solder ball tolerance of the small body nFBGA is wider than that of other similar WCSP packages. What is driving this wider tolerance?
A The WCSP has the solder ball mounted directly on the die. The nFBGA balls are mounted on the solder pad of the substrates. This pad size is driven by the solder mask opening so there is slight variation. In addition, the nominal solder ball size for the WCSP is smaller than the NFBGA. This larger ball size and variation in solder pad size are what causes there to be a wider tolerance for the nFBGA solder ball dimension.
Q Will design changes need to be made on the PCB if the package is switched from a WCSP to an nFBGA of the same size?
A No, in most cases, the recommended PCB pad size is the same for both packages so the so the same PCB can be used.
Q The small body nFBGA is slightly higher than the current package solution. Will this be an issue?
A Unless the final product has a strict height restriction, minor differences in package height (± 0.05 mm) are not significant. The only impact would be to the pick and place process. The customer would simply need to measure the actual component thickness and adjust the process accordingly. This is standard procedure for component placement setup.
Q Will any changes need to be made to the SMT process to support small body nFBGAs?
A nFBGAs can support both flux dip and paste printing SMT processes. In addition, solder balls used for nFBGAs may be larger than that of other packages so, the stencil aperture will need to be reduced.
Q Are smaller pitch sizes available?
A Currently, 0.4 mm is the smallest ball pitch that TI offers for nFBGA packages. Pitch sizes smaller than 0.4 mm are not widely used in the industry for BGA packages and would require customization of the customer PCB.