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Excessive solder balls!

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#64609

Excessive solder balls! | 8 July, 2011

Hello, I am having a problem with a large amount of solder balls surrounding mostly the legs of fine pitch ics. There seems to be a large collection in gap between the pad and the solder resist. They do not easily wash out. Our profile seems to be nailed in. Our print is also dead on. Does anyone have any ideas on what is causing this? The pictures are the best we can get.

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#64610

Excessive solder balls! | 8 July, 2011

How did you determine that your thermal recipe "seems to be nailed in"?

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#64611

Excessive solder balls! | 8 July, 2011

I profiled it using a KIC Explorer. PWI is at 60%

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#64612

Excessive solder balls! | 8 July, 2011

Check that your pick and place machine is not pushing the part too far in the paste and squeezing the paste off the pad. Your profile could need modifying. In the case of the profile the solder paste can slump off the pads before turning into a liquid. When it does change from the paste state to the liquid state it pulls back to the pad leaving solder behind or some of the paste balls left behind liquefy and condense on the board leaving balls. Before you start changing things Check your screen printing registration; keep the bottom off the screen clean to make sure you are not leaving solder paste balls deposited on the board. Check the board before the oven to make sure the paste is on the pad and not squeezed out. Remember Manufactures’ solder paste profiles are a guide line. There is a lot of physics going on when a board is going thru an oven and sometimes there is a little Black Magic involved. That’s what makes us manufacturing engines so valuable and underappreciated/(paid) sometimes

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#64613

Excessive solder balls! | 8 July, 2011

OK. You used a thermometer to to check your recipe. How do know that the temperatures that you selected are correct?

Your solder balls indicates that it's possible that the temperatures that you selected might not be correct. Without belaboring an old comment, the recipe provided by a solder paste fabricator is only the starting point for developing a final recipe.

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#64617

Excessive solder balls! | 8 July, 2011

I concur with Mr. KaHrpr and Mr. Dave. Just because your measured profile falls in the middle of a process window doesn’t mean that you won’t ever have to analyze it. You may be 9/10ths of the way there, but running 25 miles won't win you a marathon.

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#64618

Excessive solder balls! | 8 July, 2011

Thanks for all the input guys! After trying to figure this out in our smt process, we have discovered that the board house did not meet the required pad width for the fine pitched ICs when making the bare boards. Our stencil was cut out to fit the pads layed out for the gerbers causing there to be a bit of an issue. The paste was being directly deposited in the opening of the solder mask. I appreciate all of the comments!

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#64620

Excessive solder balls! | 8 July, 2011

Another happy ending! Good job on nailing down the root cause! You might just win that marathon after all. ;)

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