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TECHNET  July 2016

TECHNET July 2016

Subject:

Re: ENIG Board Finish with Tin Plated hardware

From:

Mumtaz Bora <[log in to unmask]>

Reply-To:

TechNet E-Mail Forum <[log in to unmask]>, Mumtaz Bora <[log in to unmask]>

Date:

Thu, 7 Jul 2016 19:31:41 +0000

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text/plain (1 lines)

Hi George,



Thank-you for your reply and detailed % calculations. I apologize for my late reply as I was tied up with some customer audits. I will  revise our internal procedure to reflect the change to surface mount simulation test. Again, appreciate your feedback and insight into this test method. Will the standard be revised to state that leadless packages should use surface mount reflow simulation test as assembly houses and subcontractors that use solder dip are very reluctant to change to reflow simulation method.



Regards, Mumtaz

From: [log in to unmask] [mailto:[log in to unmask]]

Sent: Tuesday, July 05, 2016 7:14 PM

To: Mumtaz Bora

Cc: Forum, TechNet; Steve Gregory

Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware



Hi Mumtaz,



Your results are what I would expect for solderability testing these QFN component:



All of the four large ground planes in the center of each of the QFNs you solderability tested wet well with solder in all three test methods (Dip-&-Look at 45 degrees, Dip-&-Look at 90 degress, and Simulated Surface Mount Reflow).  This indicates that the ENIG plating on the packages was solderable.



When you examine just the smaller interconnect pads around the perimeter you found that not all of them wet with Dip-&-Look but all of them did wet with Simulated Surface Mount Reflow.



In the attached PowerPoinT file you will see I added percentages (defect percentages for interconnection pads) to the solderability tests of the Date Code 1409 and 1606 QFN packages for each of the tests:



Dip-&-Look at 45 Degrees for Date Code 1409 QFN's  28 non-wet pads out of 150 pads = 18.7%

Dip-&-Look at 45 Degrees for Date Code 1606 QFN's 24 non-wet pads out of 150 pads = 16.0%



Dip-&-Look at 90 Degrees for Date Code 1409 QFN's 4 non-wet pads out of 150 pads = 2.7%

Dip-&-Look at 90 Degrees for Date Code 1606 QFN's 13 non-wet pads out of 300 pads = 4.3%



Simulated Surface Mount Reflow for four QFNs 0 non-wet pads out of 120 pads = 0.0%



The angle at which you did the Dip-&-Look had a big effect on the indication of solderability.  If you had seen large differences in solderability between different Date Code QFN components that might have been an indication that there really was a solderability issue with the ENIG plating.  However, all of the large pads wet with solder and the percentage of small pads that didn't wet at 45 degrees Dip-&-Look averaged 17.4% but when Dip-&-Look tested at 90 degrees averaged only 3.5%.  Clearly the Dip-&-Look testing angle had a significant impact on the testing results as did the geometry of the pads (i.e., large versus small pads).



The early issues of solderability testing procedures called out only the Dip-&-Look primarily because they were written when lots of PCBs were wave soldered and because the Dip-&-Look test was very easy to perform.  However, when components became smaller, circuit densities increased and surface mount reflow became common place and also because lots of leadless components became common place it was realized that the Dip-&-Look soldereability test was primarily a wave soldering solderability test.  That is when the Simulated Surface Mount Reflow solderability test was added to the testing procedures.  In my mind the Simulated Surface Mount Reflow test is the only test that should be used to assess the solderability of leadless components.



If you took more QFN's and Dip-&-Look tested them at 180 degrees of vibrated the packages when they were immersed in solder (regardless of the angle) I'm sure you would find addition improvements in soldering.  However, at this point I wouldn't recommend doing any additional Dip-&-Look solderability tests with the QFNs because Dip-&-Look isn't a good measure of solderability.  Stick with the Simulated Surface Mount Reflow Solderability Testing.



I know TN will strip off the PowerPoinT file but you might want to ask Steve to post it on his site





Regards,



George Michael Wenger



George M. Wenger

Failure Signature & Characterization Lab LLC

609 Cokesbury Road, High Bridge, NJ 08829

(908) 638-8771 (Home) (732)-309-8964 (Cell)

[log in to unmask]<mailto:[log in to unmask]>



________________________________

From: "Mumtaz Bora" <[log in to unmask]<mailto:[log in to unmask]>>

To: "TechNet E-Mail Forum" <[log in to unmask]<mailto:[log in to unmask]>>, [log in to unmask]<mailto:[log in to unmask]>

Sent: Tuesday, July 5, 2016 5:37:49 PM

Subject: RE: [TN] ENIG Board Finish with Tin Plated hardware



Hi George, I hope this email finds you well.

I did repeat the test using a 90 degree dip and attached are the images. The wetting improved significantly, but it was not 100%. I also reflowed the part in an table top reflow oven and wetting seemed much better. Please see attached images. Please advise if you have any comments or anything else we should follow up.



Regards, Mumtaz





















-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of George Wenger

Sent: Sunday, May 29, 2016 8:32 PM

To: [log in to unmask]<mailto:[log in to unmask]>

Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware



Michael,



I agree with Tan Geok Ang. I fully understand why your mfg/assy facility in EU is balking at the finish mismatch. However, I do not agree at all with their suggestion that you change the board finish to immersion tin. Immersion tin surface finish has serious shelf life and solderability issues and I know that sometime after you switch to immersion tin you'll be wishing you hadn't switched



Although Guideline #7 in "The TIN Commandments" published by AMP indicates "Mating tin coated contacts to gold coated contacts is not recommended.", before I would switch your board surface finish I would ask your customer if they have ever seen any issues with your boards related to finish mismatch. Since this finish mismatch is only used for mechanical mounting I don't think the finish mismatch will cause functional issues. Especially since you indicated you been using this finish mismatch for some time and if that is the case I assume someone would have seen a problem if there was one Also, there isn't much gold on ENIG surface finish (only a couple of micro-inches) and there probably won't be any considerable amount of corrosion



If my mfg/assy facility told me I had to board surface finishes I would push back really hard and tell them that if they are worried about the gold/tin finish mismatch they should just take a soldering iron and a piece of solder and "tin" the few ENIG pads on the board where the hardware is mounted (i.e,, wet the ENIG pads solder which will dissolve the small amount of gold and eliminate the finish mismatch).







Regards,



George Michael Wenger



George M. Wenger

Failure Signature & Characterization Lab LLC

609 Cokesbury Road, High Bridge, NJ 08829

(908) 638-8771 (Home) (732)-309-8964 (Cell) [log in to unmask]<mailto:[log in to unmask]>



----- Original Message -----



From: "Tan Geok Ang" <[log in to unmask]<mailto:[log in to unmask]>>

To: [log in to unmask]<mailto:[log in to unmask]>

Sent: Sunday, May 29, 2016 10:44:50 PM

Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware



In long term , ENIG with Sn will cause fretting corrosion. BUT don't change the ENIG board finish to Tin surface finish as it creates hell lots of other issue during manufacturing.





-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce Koo

Sent: Friday, 27 May 2016 11:43 PM

To: [log in to unmask]<mailto:[log in to unmask]>

Subject: Re: [TN] ENIG Board Finish with Tin Plated hardware



> "We've built all these assemblies, many, many times without issue."

you means Siemens didn't have the dissimilar metal coupling check?

Build is not an issue, corrosion in the field and resistance change might be... it is reliability issue. if your stuff only work on one shot deal (like bomb), and you just engage the two parts upon short usage life, not much of issue, if you are in the field for long time

- like more than 3 month, you should consider dissimilar metal coupling from the start of design phase - use some good material/ process engineer to select mating parts properly (according to standards).

better not be one of those electrical switches... not smart one either...

jk

On May 27, 2016, at 10:43 AM, Kuczynski, Michael wrote:



> We've been using ENIG finish for our PCB's and installing tin plated

> hardware (self clinching, broaching nuts and standoffs)

>

> We use anywhere from 1 or 2 pieces, to maybe a dozen, of this hardware

> on various assemblies.

> These items are used just to hold or mount some items in place (no

> serious stress on these items).

>

> Our mfg/assy facility in EU is balking at the finish mismatch and

> suggesting we change the board finish to immersion tin (which we've

> never used).

>

> We've built all these assemblies, many, many times without issue.

>

> Is there any other merits I should consider, before I tell them please

> build them as is?

>

>

> Michael Kuczynski

> Mgr. ECADS - Electrical 511 Benedict Ave.

> 914-524-3118 (Ph) Tarrytown, NY 10591

> 914-524-3322 (Fax) Mail Stop P25-1-C

> [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]:[log in to unmask]>>

>

>

>

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