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Solder joint srength



Solder joint srength | 10 June, 2001

I know that there is no pre-defined strength for the solder joint as it will depend on solder volume deposited, pad geometry, lead component's lead solderability etc. but, what would be the best ball park for the good joint for 0402, 0603, 20 mil ptich QFP ( pad size 12 mil & 10 mil ).

Any input will be greatly appreciated.

thank you.

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Solder joint srength | 11 June, 2001

Continuing, I�ve optioned about the uselessness of shear testing of solder connections on this forum previously. So, the points that you make about the elusiveness of developing a standard for measuring solder connection strength is well taken. I�ll add a couple of kickers. The value of strength also varies with: * Method used. * Speed of shearing the solder. * Type of solder. * Age / graininess of the solder. * Temperature of testing.

Additionally, when shearing a component, you not only apply shear stress, but also roll the component over. This means that both a shear stress and a normal stress are present, again making the results very dependent on where you apply the load.

Moving on, a properly formed solder connection is stronger than the underlying copper to laminate bond. Measuring pad peal strength: IPC-TM-650, Method 2.4.21 for multiple solderings, use Method 2.4.8 for copper peal using a Instron machine. Typical requirement for Cu is: 6 lb (force)/in [106 kg (force) /m].

Consider that periodically micro-sectioning solder connections on a coupon is probably the best approach to process control of this nature. [Realistically, it's not like a shear test represents any condition that a board is likely to encounter. Yer just tryin' to see if you soldered the little square thing to the flat thing!!!]

Alternately, get some vise grips and just torque the component from the board and then look at the terminations. A truly interfacial separation shows essentially only base metal on one fracture surface and solder on the other termination. You see intermetallic compound [IMC] rarely, because in most of these cases no metallurgical bonding (wetting = formation of IMC) has taken place. If you break the component, pull the pad, or see IMC; push on to something else [like rework].

Finally, responding directly to your question [Pfew, FINALLY!!!! ]. Look in EP&P 4/01 p 56. Average shear strengths using a 5kg load cell and a shear rate of 0.01 in/sec are: 0201/734 g; 0402/1750g; 0603/2200g.

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Solder joint srength | 18 June, 2001

Thanx Dave. What about the ball park figure for 20 & 16 mil pitch pull strength.

Appreciate your input and thank you in advance.

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