SLVAEU0 September 2020 LM117HVQML-SP , LM117QML-SP , LM136A-2.5QML-SP , LM137JAN-SP , LM137QML-SP , LM185-1.2QML-SP , LM185-2.5QML-SP , LM2940QML-SP , LM2941QML-SP , LM4050QML-SP , LM723JAN-SP , LP2953QML-SP , TL1431-SP , TPS50601-SP , TPS50601A-SP , TPS7A4501-SP , TPS7H1101-SP , TPS7H1101A-SP , TPS7H1111-SP , TPS7H1121-SP , TPS7H2201-SP , TPS7H2211-SP , TPS7H3301-SP , TPS7H4001-SP , TPS7H4002-SP , TPS7H4011-SP , TPS7H5001-SP , TPS7H5002-SP , TPS7H5003-SP , TPS7H5004-SP , TPS7H6003-SP , TPS7H6013-SP , TPS7H6023-SP , UC1525B-SP , UC1611-SP , UC1705-SP , UC1707-SP , UC1708-SP , UC1709-SP , UC1710-SP , UC1715-SP , UC1823A-SP , UC1825-SP , UC1825A-SP , UC1825B-SP , UC1832-SP , UC1834-SP , UC1842-SP , UC1842A-SP , UC1843-SP , UC1843A-SP , UC1843B-SP , UC1844-SP , UC1844A-SP , UC1845-SP , UC1845A-SP , UC1846-SP , UC1856-SP , UC1863-SP , UC1875-SP , UC1901-SP , UC19432-SP , UCC1806-SP
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Board-level solder reflow profiles are dependent on numerous factors including, but not limited to, solder type, flux, package type, the number of components, the number of board layers, the board size, reflow oven type, and accuracy as well as pre- and post-cleaning processes. Because of the number of variables it is not possible to provide a single reflow profile that is representative of every board using a specific package type. Typically, manufacturing houses have reflow profiles in place and modify them for specific hardware.
TI suggests using the flux manufacturer’s recommended profile as a starting point. Variations of course need to be comprehended based on the time required to volatize the flux prior to the solder reaching liquidus. In general, ceramic parts are compatible with ramp-up rates of < 3°C/s and ramp-down rates of < 6°C/s with a maximum peak temperature of 260°C.
A hermetic package will withstand three passes of reflow if the peak temperature and ramp rates are not exceeded.
Most metal lid packages use an 80%Au-20%Sn solder preform to attach the lid. Gold-tin solder will begin to soften at 270°C and has a eutectic point of 280°C. The package body temperature must not exceed 260°C at any time or the hermetic seal of the package will be damaged. Note that through-hole hermetic devices specify a maximum temperature for soldering as a lead-temperature of 300°C for 10 seconds. This is not a reflow temperature.
TI offers a variety of termination finishes for compliant hermetic packages, for example:
Alloy-42 leads with Sn63Pb37 hot solder dip.
Alloy-42 or Kovar leads with 50µ-in to 350 µ-in of nickel underplate and 60 µ-in to 225 µ-in of gold finish plate
Alloy-42 or Kovar leads with 50µ-in to 350 µ-in of nickel underplate and SN63Pb37 hot solder dip
Coating |
Minimum |
Maximum |
---|---|---|
Hot solder dip (for all round leads) |
60 µ-in |
Not Specified |
Hot solder dip (for all shapes other than round leads which have ≤ 25 mil pitch) |
150 µ-in |
Not Specified |
Hot solder dip (for all shapes other than round leads with > 25 mil pitch) |
200 µ-in |
Not Specified |
Tin-lead plate (as plated) |
300 µ-in |
Not Specified |
Tin-lead plate (fused) |
200 µ-in |
Not Specified |
Gold plate |
50 µ-in |
225 µ-in |
Nickel plate (electroplate) |
50 µ-in |
350 µ-in |
Nickel plate (electroless) |
50 µ-in |
250 µ-in |
Nickel cladding |
50 µ-in |
350 µ-in |
The electronics industry currently recognizes a threshold level of 3% gold by weight that can be dissolved into eutectic tin-lead solder above which the solder-joint may exhibit gold embrittlement.
With the specified gold thickness it is recommended that gold-plated leads be pre-tinned (solder-dipped) before board mounting to scavenge the gold from the leads. If this is not done, there is a chance of gold-embrittlement of the board-level solder-joints. A flowing solder-pot or two passes in a static solder-pot is recommended. Solder-pot solder composition should be periodically monitored for gold content.