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10.1.1 Component Tinning Basics

 
The above video demonstrates tinning on SOIC type components. During this video demonstration, the solder pot shroud and nitrogen inerting was removed to clearly show the tinning process.
 
Outline
The guides in section 10 cover the requirements for using manual tinning and robotic hot solder dip to replace the finish on various types of electronic components.

There are two major reasons to solder dip electronic components: solderability concerns and tin whisker mitigation. Solder dip for tin-whisker mitigation differs from solder dip for solderability in that for tin whisker mitigation the termination needs to be coated over its entire length, right up to the package surface. During solder dip, the piece part experiences temperature differences significantly greater than those present during typical board-level assembly. In addition, the fluxes used during the dipping process can become trapped in a minor delamination, like that commonly found in plastic piece parts, which can lead to reliability issues. To avoid these concerns, the solder dip process needs to be qualified and carefully controlled.

To decrease the possibility of failure of the electronic components after being solder dipped and to ensure a quality process is performed each time, requirements for performing robotic hot solder dipping are included in section 10.

These guides cover the replacement of pure tin and Pb-free tin alloy finishes with tin-lead (SnPb) finishes for subsequent assembly with tin-lead solder. The guides in section 10 may also be applicable to other component lead finish changes. Replacement finishes other than SnPb should be evaluated for tin whisker mitigation prior to implementation.

Caution
Due to the need to completely control the rates of immersion and emersion of the component terminations and the dwell times in and between each process step, robotic hot solder dip is recommended for electronic component tinning. Semi-automatic or purely manual solder dipping processes may not be capable of completely controlling the rates of immersion and emersion of the component terminations and only provide approximate dwell dipping times in the solder bath. Greater variation in the process may cause a higher chance of damage, including latent reliability problems. Manual dipping required for full finish replacement is different than manual dipping currently practiced for meeting solderability requirements because of the increased need for 100% coverage all the way to the component body to prevent whisker growth. Certain electronic component package styles may not lend themselves to robotic hot solder dipping and may require alternative processing.

Note
For detailed information refer to GEIA-STD-0006 Requirements for Using Robotic Hot Solder Dip to Replace the Finish on Electronic Piece Parts.

GEIA-STD-0006 defines the requirements for fully replacing undesirable surface finishes using robotic hot solder dip. Requirements for qualifying and testing the refinished components are also included. This standard covers the replacement of pure tin and Pb-free tin alloy finishes with SnPb finishes with the intent of subsequent assembly with SnPb solder. This standard covers process and testing requirements for a robotic dipping process and does not cover semi-automatic or purely manual dipping processes.

GEIA-STD-0006 does not apply to component manufacturers who originally build components with a hot solder dip finish. It applies to refinishing performed by a robotic hot solder dip service supplier or production facilities at the customer, whenever the intent of the dipping is to have full coverage and replacement of Pb-free tin. Replacement of BGA spheres or CGA columns is not included in the scope of this standard. IEC TS 62647-4 may be used for the replacement of BGA spheres.

GEIA-STD-0006 is for suppliers and customers to incorporate these requirements into their operations to provide a consistent and well-controlled process for product applications that require significant control. Complete conversion of termination finishes from pure tin or Pb-free solder to SnPb will allow the use of electronic components for any of the Control Levels of GEIA-STD-0005-2 without mitigations. In addition to the elimination of tin whisker risks, electronic components processed to this standard will also exhibit enhanced solderability and solder joint reliability compared to most COTS finishes.

Requirements for Robotic Hot Solder Dipping Apparatus
Robotic Hot Solder Dipping Apparatus shall include the following.
  • Feature a vacuum or mechanical pickup mechanism
  • Not damage the piece part or its terminations
  • Not utilize metal surfaces that may scratch or cause solder smears
  • Be capable of controlling the dwell time in the pre-heat and solder pot within ±0.1 second
  • Be capable of controlling the exit speed out of the solder pot to within ±0.12 inch (0.3 cm)/s
  • Be capable of controlling the depth of immersion to within ±0.004 inch (0.01 cm)
  • Ensure dipping of the full termination or other tin or Pb-free tin finished surface into the solder pot including the side of the package (if applicable)
Apparatus for Gull-Wing Formed Leads
In addition to those requirements above, the dipping apparatus used for robotic hot solder dipping gull-wing formed leads shall also be capable of edge dipping the piece parts with the following controls:
  • Solder dip immersion angle and direction of travel
  • Solder dip withdrawal angle and direction of travel
  • Ability to rotate piece part to allow each side to be solder dipped independently
Apparatus for J-Leaded Formed Leads
In addition to those requirements above, the dipping apparatus used for robotic hot solder dipping J-lead formed leads shall be capable of edge and planar dipping the piece parts to cover neighboring termination surfaces not obstructed by the package body.

Overall Process Flow
  1. Qualification of Process - Prior to production, qualification of the refinishing process shall be performed in accordance with GEIA-STD-0006.
  2. Dry Bake - The MSL of piece parts shall be obtained/verified from/by the customer. All piece parts with MSL 2 or greater shall be dry baked before refinishing in accordance with J-STD-033. Dry bake is not required for electronic components received in labeled dry bags with desiccant and humidity indicators reading less than 5% RH or for electronic components Type 1. Once the packaging has been opened it shall be handled in accordance with J-STD-033. Moisture-sensitive electronic components received in unknown conditions shall be dry baked in accordance with J-STD-033. The cumulative bake time limits of J-STD-033 shall not apply to baking prior to refinishing.
  3. Fluxing - The flux used shall be in accordance with GEIA-STD-0006 or customer requirements and shall be applied to the piece parts in a consistent and repeatable manner.
  4. Preheat - Components shall be preheated prior to robotic hot solder dipping. Preheat ramp-up rates shall not exceed the original piece part manufacturer's specifications, J-STD-020, J-STD-075, or as specified on engineering documentation.
  5. Application of Solder - After flux and preheat, the component part terminations shall be immersed in the molten solder by a robotic hot solder dipping apparatus. The total time in solder shall not exceed 5 seconds per immersion. A dynamic wave or another method that removes solder dross shall be used.
  6. Cool Down, Cleaning, and Drying Methods - Cooling rates shall not exceed the component manufacturer’s specifications, J-STD-020, J-STD-075, or as specified on engineering documentation. Cleaning shall be performed within 1 hour of solder dipping in accordance with the flux manufacturer's recommendations or in accordance with J-STD-033, J-STD-075, where applicable. Drying shall be accomplished in a manner to prevent re-deposition of ionic material onto the electronic components or reduction of solderability of the component.
  7. Rework - Piece parts within the production lot shall not be reworked more than TWICE. A single rework process is defined as one complete throughput through the robotic hot solder dipping process for any combination of package side(s) after the initial robotic hot solder dip. Any piece parts damaged shall be segregated, marked as defective, and returned to the customer; this includes piece parts dropped into the solder pot or on the floor or exhibiting physical damage after a fall.
  8. Inspection and Testing - Electronic components shall be tested in accordance with applicable test methods defined in GEIA-STD-0006 or as defined by customer drawings. If there are any failures during applicable test methods of the production lot testing then the customer shall be notified. Failed tested electronic components shall be segregated, marked as defective, and returned to the customer. Production electronic components of failed lots shall be identified and returned unless screened for the defect found in the sample devices.
  9. Post-Process Baking - After all processing and inspection, electronic components that were dry baked shall be dry baked again in accordance with J-STD-033 and dry packaged in moisture barrier bags. The cumulative bake time shall be reset to "zero" upon final packaging.


Acceptability References
IPC-A-610 Acceptability of Electronic Assemblies
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
IPC J-STD-033 Joint Industry Standard for Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Device
J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies
J-STD-020 Moisture/Reflow Sensitivity Classification for Nonhermetic Surface Mount Devices
GEIA-STD-0006 Requirements for Using Solder Dip to Replace the Finish on Electronic Piece Parts
Manufacturer's Datasheets Requirements for case temperature maximum and Moisture Sensitivity Level (MSL)
Procedure for reference only.