NXP Semiconductors AN10365 Application Note
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NXP Semiconductors AN10365 Application Note

NXP Semiconductors AN10365 Application Note

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AN10365
Surface mount reflow soldering description
Rev. 03 — 22 April 2008
Document information
Info
Keywords
Abstract
Content
surface mount reflow soldering
This application note provides guidelines for the board mounting of IC
packages.
Application note

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Summary of Contents for NXP Semiconductors AN10365

  • Page 1 AN10365 Surface mount reflow soldering description Rev. 03 — 22 April 2008 Application note Document information Info Content Keywords surface mount reflow soldering Abstract This application note provides guidelines for the board mounting of IC packages.
  • Page 2 AN10365 NXP Semiconductors Surface mount reflow soldering description Revision history Date Description 20080422 various text amendments to Section 1, 2.1, 2.2, 2.3, 3, 4.1, 4.2, and 6. 20060726 updates in Table 1, Table 8 and on page 20: the minimum peak reflow temperature when using SnPb solder is changed from 210 °C to 215 °C...

  • Page 3: Introduction

    AN10365 NXP Semiconductors Surface mount reflow soldering description 1. Introduction This application note provides guidelines for board mounting of surface mount IC packages. Nowadays, reflow soldering is a widely spread technology for soldering of surface mount IC packages. For some of the newer IC packages, such as Ball Grid Arrays (BGAs), reflow soldering is the only suitable method.
  • Page 4 NXP Semiconductors packages can be found by clicking ‘Package Information’ on the ‘Product Information’ page of the NXP Semiconductors web site at the URL given in “Contact information” at the bottom of page 2. The unique identifier for the PCB footprint is the NXP package outline code (the package SOT number).
  • Page 5 AN10365 NXP Semiconductors Surface mount reflow soldering description Footprint information for reflow soldering of SSOP20 package SOT266-1 (0.125) (0.125) D2 (4x) Generic footprint pattern Refer to the package outline drawing for actual layout solder land occupied area DIMENSIONS in mm 0.650...
  • Page 6 The real package outline (with the correct number of terminals) can be found under ‘Package information’ on the ‘Product information’ page of the NXP Semiconductors web site at the URL given in “Contact information” at the bottom of page 2.

  • Page 7: Ic Packages

    AN10365 NXP Semiconductors Surface mount reflow soldering description Note that a solder resist defined layout requires the application of a solder resist bridge between two terminals. There is a minimum width of solder resist that can be applied by board suppliers. This fact, in combination with a maximum solder resist placement accuracy, implies that solder resist defined layouts are not always possible.
  • Page 8 AN10365 NXP Semiconductors Surface mount reflow soldering description leads terminal types solder balls lands (leadless) 001aac834 Fig 6. Package types Leaded packages (e.g. SO and QFP) • With leaded packages, coplanarity is an important issue; coplanarity must be within the specifications (refer to the package outline drawing) in order to prevent the occurrence of open circuits or bad joints;...
  • Page 9 AN10365 NXP Semiconductors Surface mount reflow soldering description 001aac836 Fig 8. Example of a BGA Leadless packages with solder lands (e.g. HVQFN and HVSON) • The exposed lead frame edges at the sides of the IC packages are often not finished - these do not have to be wetted for a proper joint •...

  • Page 10: Solder Paste

    AN10365 NXP Semiconductors Surface mount reflow soldering description 2.3 Solder paste In line with european legislation, it is recommended to use lead-free solder paste, although exemptions are granted for selected applications, such as automotive. A wide variety of Pb-free solder pastes is available, containing combinations of tin, copper, antimony, silver, bismuth, indium, and other elements.
  • Page 11 AN10365 NXP Semiconductors Surface mount reflow soldering description 001aac839 Fig 10. Example of MSL information on sticker; note the two MSLs, corresponding to the two reflow processes An MSL corresponds to a certain out-of-bag time (or floor life). If IC packages are removed from their sealed dry-bags and not soldered within their out-of-bag time, they must be baked prior to reflow, in order to remove any moisture that might have soaked into...

  • Page 12: Surface Mounting Process

    AN10365 NXP Semiconductors Surface mount reflow soldering description 4. Surface mounting process 4.1 Solder paste printing Solder paste printing requires a stencil aperture to be completely filled with paste. Then, when the board is released from the stencil, the solder paste is supposed to adhere to the board, so that all of the paste is released from the stencil aperture, and a good solder paste deposit remains on the board.
  • Page 13 AN10365 NXP Semiconductors Surface mount reflow soldering description narrow enough, it will snap open during reflow, as the volume of molten solder seeks to attain minimum surface area. A wider bridge, however, may remain stable, resulting in a short-circuit. To achieve a difference in solder paste volumes on one board, it is possible to use a stencil that has a different thickness at different locations.
  • Page 14 AN10365 NXP Semiconductors Surface mount reflow soldering description 001aac842 001aac862 Fig 13. Paste coverage Fig 14. Pattern coverage The paste printing pattern for exposed die pads is illustrated with an example, see 15. A HVQFN48 with an exposed pad of 5.1 mm × 5.1 mm, for example, should Figure have nine solder paste deposits that are arranged in a three-by-three array.

  • Page 15: Ic Package Placement

    AN10365 NXP Semiconductors Surface mount reflow soldering description Keep in mind that printing a smaller volume of solder paste could have adverse effects on the solder joint reliability. Also, if there are vias in pads, solder paste deposits should be arranged so that paste is never printed directly over a via.

  • Page 16: Reflow Soldering

    AN10365 NXP Semiconductors Surface mount reflow soldering description Therefore, the placement force must always be adjusted so that there is no excessive paste bulging or even splattering and there is a proper contact between the IC package and the solder paste. The necessary placement force to achieve this will depend on a number of factors, including the package dimensions.
  • Page 17 AN10365 NXP Semiconductors Surface mount reflow soldering description will also reduce the local temperature. Hot spots, on the other hand, are found in areas with few components, or only the smallest components, and with little Cu. Finally, the board dimensions, and the board orientation in the oven, may also affect the location of hot and cold spots.

  • Page 18: Solder And Terminal Finish Or Solder Ball Compatibility

    AN10365 NXP Semiconductors Surface mount reflow soldering description When reflow soldering, the peak temperature should never exceed the temperature at which either the components or the board are damaged. The maximum peak temperature for components is partially determined by their moisture sensitivity. For reflow soldering with SnPb solder, the peak temperature should be higher than 215 °C;...

  • Page 19: Inspection And Repair

    AN10365 NXP Semiconductors Surface mount reflow soldering description This, however, is not the case for packages with solder balls. If these packages are soldered, the IC package solder balls and the solder paste both melt, to form a single joint.

  • Page 20: Repair

    AN10365 NXP Semiconductors Surface mount reflow soldering description 001aac846 001aac863 a. SnPb solder joints b. Pb-free solder joints Fig 18. Difference in wetting between SnPb and Pb-free solder joints Another visual aspect in Pb-free soldering is that Pb-free solder joints tend to be less shiny than SnPb solder joints, and they may have striation marks.

  • Page 21: Device Removal

    AN10365 NXP Semiconductors Surface mount reflow soldering description 5.2.1 Device removal In order to remove an IC package from the board, it must be heated; if possible, this must be done as locally as possible, to avoid heating the surrounding board and components.

  • Page 22: Solder Paste Printing

    AN10365 NXP Semiconductors Surface mount reflow soldering description 5.2.3 Solder paste printing After the site redress is completed, solder paste should be applied to either the site or the device. This can be done by using a miniature stencil or other in-house techniques.

  • Page 23: Legal Information

    Notice: All referenced brands, product names, service names and trademarks information. are the property of their respective owners. Right to make changes — NXP Semiconductors reserves the right to make changes to information published in this document, including without limitation specifications and product descriptions, at any time and without notice.

  • Page 24: Table Of Contents

    AN10365 NXP Semiconductors Surface mount reflow soldering description 9. Contents Introduction ......3 Materials .

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