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I wonder about space-grade ICs in flat packages.

Space-grade flat package ICs have very long leads compared to the commercial versions.

If I use a flat package IC on my CubeSAT board, can I modify the lead length by cutting or bending?

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Yes, some space-grade flat-pack packages are manufactured with long leads. The user is expected to cut/bend them to meet their specific environmental needs. Longer leads may be necessary for severe vibration, shorter leads to save board space.

You should use a proper lead-forming tool. You don't want to apply stress to the joint where the lead meets the package.

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If it is non military and commercial yes you can but it needs to be done properly. You need to support the leads between the package and the bend and then for the cut. This is to prevent shock going back into the IC causing damage. The procedure was in many data books if you can still find one.

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    \$\begingroup\$ Lead-forming is still done on flat-packs used in military applications. \$\endgroup\$
    – Ryan
    Oct 7, 2022 at 12:13
  • \$\begingroup\$ I'm not sure the shock of lead cutting is a problem with plastic encapsulated parts, though it is still a good practice. The problem I think Gil mentioned was with ceramic packages, that had a glass seal where the leads entered the package. It is this glass seal that was susceptible to damage, not the IC. \$\endgroup\$
    – SteveSh
    Oct 7, 2022 at 14:06
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The main reason for using leaded parts in mil/space applications is because of the stress that's applied to the solder joints during operational temperature swings. Too much stress, or too much accumulated stress (repeated application of a small amount of stress) can cause the solder joints to fail.

The material that the IC (and it's package) is made of usually has a different CTE (coefficient of thermal expansion) than does the PWB on which it's mounted. This difference in CTE puts stress on a rigid solder joint when the temperature changes.

These temperature changes can be due to environmental factors (into and out of the earth's shadow, for instance) or operation factors (an IC heats up when it's tuned on, relative to the PWB).

So in order to reduce this stress that accumulates over many temperature cycles - tens of thousands depending on a satellite's orbit and mission - you want some compliance, or give, between the leads and the PWB. A leaded part provides this compliance.

Note that this may not be a problem for a typical Cubesat application, which usually have a limited expected on-orbit life (several months to a year).

Usually leaded parts are not needed for vibration or shock reasons, which tend to be short duration for a satellite. Just the opposite, parts that might be shown to separate from the PWB during shock or vibe may be expoxyed or otherwise fastened to the board.

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  • \$\begingroup\$ Agree that temperature cycling is also an issue. But, some launch vehicles create a lot of vibration, and some conservative customers add excessive margin. I worked on a program with 20g vibration launch requirements. \$\endgroup\$
    – Mattman944
    Oct 8, 2022 at 16:08
  • \$\begingroup\$ Just saying you have a 20g vibe launch environment really doesn't mean much. You also need to know the vibration spectrum, or the vibe profile. If the 20g is at a frequency far removed from the natural frequency of the mounted component, then you have nothing to worry about. \$\endgroup\$
    – SteveSh
    Oct 8, 2022 at 16:44

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