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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


0201 caps

James Lewis

#22562

0201 caps | 2 December, 2002

In doing process qualifications for 0201 caps, has anyone taken cross-sections and discovered cracks / hairline fractures / voids between the metalization on the end and the ceramic itself? (not cracks in the solder joint) We are well within the cap manufacturer's reflow profile for both ramp up and cool down guidelines, and yet we are seeing what we think is a defect, a crack that indicates seperation of the metalization between the bottom side of the termination and the ceramic itself?

Anyone been here / done this??

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#22571

0201 caps | 2 December, 2002

Sounds like you're killing the poor little critters. Tell us about: * Placement force. * Reflow method. * Where and how you are measuring your reflow recipe. * Cooling rate of the reflow recipe. * How the solder connection to the metalization appears [ie, amount of solder, height of fillet, etc.]. * Method used to depanel the board and distance and orientation of damaged capacitors are from the board edge. * Distribution of the problem.

A picture of the sectioned MLCC would be nice.

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James Lewis

#22575

0201 caps | 3 December, 2002

I don't think I can post pics in this (if anyone knows otherwise let me know), so I will email them to anyone who's curious.

Here's the answers to your questions:

Placement Force: 0201s are placed on the Siemens S23s with 1 newton of force. The separation is at the metal to substrate so I doubt it is from placement force. Reflow method: BTU Paragon 150. 10 Zone, Nitrogen Inerted, Convection Ovens.

Where and how are you measuring Reflow recipe: Attaching a thermal couple to an 0201 is next to impossible. They are like grains of sand. I attach thermal couples to the laminate in the area of the 0201s.

Cooling rate of the Reflow recipe: The cooling rate of the laminate is 2-3 C/sec. The cooling rate of the air is 4-5 C/sec. I can slow it down more but according to the component manufacturer we are well within spec.

How the solder connection to the metalization appears: See pics. Solder is beautiful. Joints look great and the wetting angles are dead on.

Method used to depanel the board and distance damaged capacitors are from the board edge: On the first 4 builds they (lab) depanelized (for cross-section prep) with a band saw. We asked for a diamond blade on the last build and the separation was even more severe.

Distribution of the problem: Not sure. I�ve asked to lab to give us feedback on the distribution to see if we can identify a trend.

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#22584

0201 caps | 3 December, 2002

Q1:A picture of the sectioned MLCC would be nice. A1: I don't think I can post pics in this (if anyone knows otherwise let me know), so I will email them to anyone who's curious. R1: You�re correct. You cannot post pix on SMTnet. Please email me the pix.

Q2: Placement Force A2: 0201s are placed on the Siemens S23s with 1 newton of force. The separation is at the metal to substrate so I doubt it is from placement force. R2: You�re correct. Placement force related cracking usually appears in the center of the MLCC, unless there are debris or something that makes the pads unequal heights.

Q3: Reflow method A3: BTU Paragon 150. 10 Zone, Nitrogen Inerted, Convection Ovens.

Q4: Where and how are you measuring Reflow recipe A4: Attaching a thermal couple to an 0201 is next to impossible. They are like grains of sand. I attach thermal couples to the laminate in the area of the 0201s. R4: Measuring the laminate in the area of the 0201 should be hotter than the component. So, if you�re keeping the laminate within the fabricator�s recommendations and getting good flow, then you�re probably fine.

Q5: Cooling rate of the Reflow recipe A5: The cooling rate of the laminate is 2-3 C/sec. The cooling rate of the air is 4-5 C/sec. I can slow it down more but according to the component manufacturer we are well within spec. R5: So if the laminate is cooling at 2-3 C/sec, then we�d expect the MLCC is cooling slower than the laminate, certainly not cooling faster than the laminate.

Q6: What is the appearance of the solder connection to the metalization A6: See pics. Solder is beautiful. Joints look great and the wetting angles are dead on. R6: If they look GREAT and there is not too much solder, then probably the problem is elsewhere.

Q7: Method used to depanel the board and distance damaged capacitors are from the board edge A7: On the first 4 builds they (lab) depanelized (for cross-section prep) with a band saw. We asked for a diamond blade on the last build and the separation was even more severe. R7: So if the lab is using a band saw, then flexure of the board during depaneling could be damaging these parts.

Q8: Distribution of the problem A8: Not sure. I�ve asked to lab to give us feedback on the distribution to see if we can identify a trend.

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#22592

0201 caps | 4 December, 2002

How about building a panel and checking it out prior to sawing it up?

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#22598

0201 caps | 4 December, 2002

As you say, some BIG time force has pulled the metalization from the bottom of the component termination. From the pix it's hard to say whether it was caused by either: * Mechanical flexure of the board during an unusual heating or other processing step. [We kind of ruled-out the thermal recipe used in reflow soldering in earlier postings on this thread as the culprit.] ... OR * Defective parts damaged during routine manuacturing processing.

I'm inclided towards the "mechanical flexure" option because some of the pix show damage to the ceramic. This cracking damage is in addition to the pulling-away of the termination metalization from the MLCC. In a couple of instances, the pictures show a 45* crack in the ceramic. Thermal or mechanical bending of boards often cause MLCC to crack like this.

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