SMD pad definition may cause solder joint cracking under extreme fatigue conditions.

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Two types of land patterns used for surface mount pads are n... - Feb 02, 2023 by Charles Nguyen

Perhaps google this, as you will find very interesting artic... - Feb 02, 2023 by MagyarT

The September 29, 2022 Express Newsletter [ https://smtnet.c... - Feb 06, 2023 by davef

Thank you for the above information but what I want to talk ... - Feb 08, 2023 by Charles Nguyen

Read the articles everyone else recommend. I haven't read of... - Feb 17, 2023 by SMTA-64387083 SMTA

Charles Nguyen

#88898

SMD pad definition may cause solder joint cracking under extreme fatigue conditions. | 2 February, 2023

Two types of land patterns used for surface mount pads are non-solder mask defined or NSMD pads and solder mask defined or SMD pads.Each type has its own advantages and disadvantages. There is a statement that SMD pad type may introduce stress concentration points that may result in solder joint cracking under extreme fatigue conditions. Can someone explain this to me? Thanks a lot.

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MagyarT

#88899

SMD pad definition may cause solder joint cracking under extreme fatigue conditions. | 2 February, 2023

Perhaps google this, as you will find very interesting articles. For scientific explanation look up solder fatigue on Wikipedia with references added. A more in depth explanation you can find on the Digikey forum where you will find other people like you looking for answers. If it was down to me, if I would design pads, I would look at what solder will be used, what is the purpose of the product (will there be extreme temperature changes, mechanical vibration, mechanical load, etc), datasheet of the solder paste which should give you yields to go by after reflow. These will give you enough overview regarding whether your solder joints will be exposed to any threat like cracking under extreme fatigue. Regards, Tamas

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davef

#88902

SMD pad definition may cause solder joint cracking under extreme fatigue conditions. | 6 February, 2023

The September 29, 2022 Express Newsletter [ https://smtnet.com/express/index.cfm?fuseaction=archives&issue=20220929 ] has papers on chip cracking

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Charles Nguyen

#88917

SMD pad definition may cause solder joint cracking under extreme fatigue conditions. | 8 February, 2023

Thank you for the above information but what I want to talk about is the PCB design aspect. Should there be any warning about it in the DFM?

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SMTA-64387083

#88977

SMD pad definition may cause solder joint cracking under extreme fatigue conditions. | 17 February, 2023

Read the articles everyone else recommend. I haven't read of them but I will say this. A Solder Mask Defined pad is a copper flood that has much more thermal mass than a Non-Solder Mask Defined pad so it will heat and cool at a slower rate. I suspect it is possible, during the cooling stage, that the solder solidifies before the pad has finished contracting which would stress the joint. There are other reasons not to use mask defined pads such as solder volume and tombstoning, I'd recommend avoiding them.

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