Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Big Holes (no Pun intended) in the IPC610D Criteria for Shrink/t

Views: 3818

#39779

Big Holes (no Pun intended) in the IPC610D Criteria for Shrink/t | 17 February, 2006

I have Immersion Ag and Immersion Sn LF boards that were waved using SAC305 alloy. I have a lot of tears/shrink voids in the waved connections. I am aware that SAC305 in wave has a propensity of shrink tears/voids due to the non eutectic property of SAC.

IPC 610 Rev D 5.2.11 says that as long as the bottom of the tear is visible, and the tear does not contact any lead land or barrel wall, it is acceptable. My issue is that clearly IPC did not put any thought in this statement. For starters, what magnification should I use for inspection of this tear? The physical appearance of these tears is such that it is impossible to be able to see the bottom (they branch out inside in a zigzag manner, and are seldom just straight down). The location of these tears may prove conductive to crack propagation during thermal cycling.

In view of this uncertainty, how do I pass these joints and ship the boards (Currently, I am in the process of x-sectioning the joints to determine the distribution and extent of these cracks in the solder to gather more info and pass/fail the boards based on it)

Any thoughts everybody???

reply »

Cmiller

#39800

Big Holes (no Pun intended) in the IPC610D Criteria for Shrink/t | 18 February, 2006

Switch to SN100C (no pun intended). I cant help with the SAC 305 issues but we should have a wave with SN100 running very soon. I will let you all know how that goes.

Please report back on the x-sectioning and share the results. I have heard some very bad things about SAC 305 as far as the cracks/tears. I have not seen any problems with SAC 305 in reflow though.

reply »

Loco

#39806

Big Holes (no Pun intended) in the IPC610D Criteria for Shrink/t | 20 February, 2006

For visual inspection table 1-2 seems to be in order here. If you can not see the bottom using 1.8 and table 1-2, it clearly would be a defect and rework would be the only option

Well, my thoughts anyway, wonder if someone has other thoughts on this.

reply »

#39814

Big Holes (no Pun intended) in the IPC610D Criteria for Shrink/t | 20 February, 2006

Great work Amol,

Please keep us posted about the results of the x sectioning. I personally don't believe that the cracks are due to non-eutectic properties of SAC. Because the alloy is only 4�C off eutectic and when a solder joint exits the solder wave there is an immediate drop in temperature of 100�C. so being off 4�C is a minor issue. One of the biggest differences between leaded and lead-free alloys is that leaded alloys are ductile (elastic) and the high tin alloys are brittle, more susceptible to cracks under stressed conditions. When a board passes over a solder wave there is a tremendous amount of thermal stress applied to the board. The board warps when in contact with the wave and goes straight again when leaving the wave. When the board exits the wave and goes from warp condition to straight the solder joint is already solid and the stress applied to the board might be the cause for the cracks with the high tin alloys (again my personal opinion).

I just hope that when a test flight is done with the lead-free/VOC free airplane they will put all the European politicians (responsible for this mess) in it and conduct the flight over the ocean so no innocent people get killed.

reply »

SMT Machines

PCB X-Ray Inspection