Hi Joyce - LOL, you should see the amount of embedded debris you leave on a
surface (and I have the SEM images to prove it)? Additionally, what
chemical composition control do you have on the eraser? Based on the data
and testing we have conducted, I would not be using erasers as a cleaning
media for any high performance product where life, safety, or long term
durability performance is needed. Perhaps for an industrial application.
Dave
On Fri, Dec 22, 2017 at 11:39 AM, Yuan-chia Joyce Koo <[log in to unmask]>
wrote:
> respectably disagree. non-sulfur containing rubber eraser are great to
> clean up plating surfaces (not immersion type, but electro-plated or
> electroless)... surface oxide layer some times is formed due to lazy chaps
> raise the unit too late (after shut down the electricity) or leave it too
> long before rince... eraser are great to recover zif, wire bonding pads,
> etc... (provide your plating pass the 3M tape test - enough adhesion to the
> under lying metallization). IMHO. as for immersion type, agree with dave
> - too thin and too soft - you might have debris embedded in the surface
> layer cause you problem...
> jk
> On Dec 22, 2017, at 8:52 AM, David Hillman wrote:
>
> And I'll third that vote! All of the immersion type finishes have roles to
>> play for our electronic designs but ImSn is the least robust to assembly
>> processes. Also, I don't recommend ever using an eraser for "cleaning" a
>> pad. If you examine a pad that has been erased, you will find eraser
>> contamination embedded in the pad that can cause solder joint integrity
>> issues later. Using an eraser to troubleshoot is ok but no further use
>> should be conducted.
>>
>> Dave
>>
>> On Thu, Dec 21, 2017 at 7:42 PM, George Wenger <[log in to unmask]>
>> wrote:
>>
>> Tan Geok,
>>>
>>> The one think I absolutely agree with is that I also hate immersion tin
>>> surface finish
>>>
>>> George
>>>
>>> -----Original Message-----
>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang
>>> Sent: Thursday, December 21, 2017 8:15 PM
>>> To: [log in to unmask]
>>> Subject: Re: [TN] BGA pad non-wetting
>>>
>>> Believe it is Immersion Sn surface finish. I usually use a pencil eraser
>>> to
>>> slightly rub against those pads and it works well. I hate immersion Sn
>>> finish. Take care of ESD.
>>>
>>> ________________________________
>>>
>>> From: Guy Ramsey <[log in to unmask]>
>>> Date: 22 December 2017 at 6:01:45 AM SGT
>>> To: [log in to unmask] <[log in to unmask]>
>>> Subject: Re: [TN] BGA pad non-wetting
>>>
>>> Wow, thanks
>>>
>>> On Thu, Dec 21, 2017 at 4:58 PM, Stadem, Richard D
>>> <[log in to unmask]> wrote:
>>>
>>> I agree with George that these pictures exhibit classic black pad or
>>>> immersion tin intermetallics of some type, but even with those some
>>>> wetting normally takes place on any given pad.
>>>> I do not think it is a thin soldermask film on the pads, but it could
>>>> be.
>>>> The reason I don't think it is soldermasking is because if you look
>>>> carefully at the picture, some pads appear to be fully wetted, and
>>>> some do not, but no pad has any partial wetting.
>>>> It is either "on" or "off". However, the pads that appear wetted may
>>>> not really be wetted. As Werner Englemaier once pointed out, you can
>>>> achieve complete "wetting" of solder on a toothpick if you know how.
>>>> But at $45,000 per assembly, it would be a career-enhancing move to
>>>> find a way to clean up the oxidation, whatever the cause. I have a
>>>> process that has worked for me, tell you in a minute.
>>>> But before you attempt to clean up any oxidation, please make one more
>>>> check. See if the pads that never wetted are connected to power,
>>>> ground, or reasonably heavier traces than the pads that DID wet, or at
>>>> least appeared to wet.
>>>> The root cause may be a perfect storm of insufficient heat in the
>>>> reflow profile, right on the edge of getting the board hot enough to
>>>> reflow unattached pads or pads not severely heatsinked, along with
>>>> some finish-related oxidation issues, and perhaps a flux not quite
>>>> active enough to remove the oxides at the current reflow temperature.
>>>>
>>>> Otherwise, I have used very fine Dremel #463 blue-oxide abrasive tips
>>>> impregnated with abrasive to remove oxides, rough areas, small burrs
>>>> and scratch marks. See one here:
>>>>
>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.google.com_se
>>>> arch-3Frls-3Dcom.microsoft-253Aen-2DUS-253AIE-2DSearchBox-26ei-3D&d=Dw
>>>> IFaQ&c=nvOEfClv88r3To4eOyYtQN0213v_-JGWbujap2hCee4&r=-MAMt3MrjiRvYJiwV
>>>> eFoas7eghr5IF6QpUBreyGR1qs&m=ZtT8m__jsmKXx-NxB6DAVryCAm8iznmmCFPq9PL_Q
>>>> qE&s=80pAGk1ZIDMwG9Yl4yta_g7WK1A6ibC-_9lxLJZVSmM&e=
>>>> LCI8WrLkFIiJ0gK3p6YCw&q=Dremel+blue+rubber+polishing+
>>>> tips&oq=Dremel+blue+rubber+polishing+tips&gs_l=psy-ab.3..
>>>> .3284.20303.0.21161.40.39.0.1.1.0.263.5212.0j26j4.30.0....0.
>>>> ..1c.1.64.psyab..9.28.4637...0j0i10k1j0i131i67k1j0i131k1j0i
>>>> 67k1j0i22i30k1j0i22i10i30k1j33i22i29i30k1j33i21k1j33i160k1.0.Sug1ul99S
>>>> sE
>>>>
>>>> They have a tiny yet firm point to clean pads of oxides or other
>>>> contamination. It takes a very fine touch to do it, is difficult on
>>>> pad diameters smaller than .020", but it can be done and for a single
>>>> component it takes less than a minute or two on the unwetted pads
>>>> only. An overhead ionizer is used to prevent or minimize any ESD
>>>> charge buildup, and the area to be reworked is masked off prior to the
>>>> polishing such that only the BGA pads are exposed. A vacuum with a
>>>> grounded tip is used to clean up the debris as you go along. Then you
>>>> wipe the area with a drop of IPA on a foam swab, and you apply a thin
>>>> veneer of a good tacky flux like Alpha WS820 immediately after the
>>>> last vacuuming. You then manually solder coat the pads, leave the flux
>>>> on but add a little more, place the part and reflow with a hot
>>>> nitrogen reflow machine. When finished, unmask under the ionizer,
>>>> prewash by directing a low pressure spray under all four sides of the
>>>> BGA, then follow that with a pass through the in-line or batch
>>>> cleaner, blow off the water at 30 PSI max (but thoroughly), bake at
>>>> 105 C for just
>>>> 20 minutes, visually inspect using a good scope and prism, and
>>>> re-test. If it passes, touchup the coating if present.
>>>> If this seems to work, perform some type of thermal cycling that makes
>>>> sense for the final use environment on two or three CCAs to ensure the
>>>> oxidation or reaction does not re-occur over time. Get the customer
>>>> buy-in if selling those units as downleveled CCAs.
>>>> If that all seems to work, then continue with the rework on a larger
>>>> sample of CCAs and closely monitor the BGA performance at test and
>>>> final visual inspection using a good microscope and prism.
>>>> No problems? Increase the sample size of the rework and continue.
>>>> Everything still good? Then walk upstairs and barge into the Upper
>>>> Management Meeting and tell them you deserve at least a 50% increase
>>>> in salary, a corner office, and a company car with expense account if
>>>> they want you to continue to keep the entire company from washing down
>>>> the toilet just when Donald was about to give them a huge tax break.
>>>> Let us know how it goes!
>>>>
>>>> Good Luck, and Merry Christmas!
>>>>
>>>> Odin
>>>>
>>>> -----Original Message-----
>>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of George Wenger
>>>> Sent: Thursday, December 21, 2017 2:05 PM
>>>> To: [log in to unmask]
>>>> Subject: Re: [TN] BGA pad non-wetting
>>>>
>>>> Steve,
>>>>
>>>> I just went back and re-read your initial post and looked at the
>>>> pictures again. I originally thought we were looking at the pads on
>>>> the BGA but now I think we're looking at the pads on your PCBA. If
>>>> they are the pads on the PCBA then my suggestion is to look at a new
>>>> non-soldered PCBA and let us know if the pads look like gold or tin.
>>>> If they look like gold you have an ENIG Black Pad problem if they look
>>>> like tin then you have an oxidized Cu-Sn IMC. The real problem in
>>>> either case there really isn't a reasonable fix. The only think I
>>>> would try is to use a very aggressive flux and try to pre-tin the pads
>>>> with solder and then clean off the flux residue and go back through your
>>>>
>>> normal repair process.
>>>
>>>>
>>>> George
>>>>
>>>> -----Original Message-----
>>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of George Wenger
>>>> Sent: Thursday, December 21, 2017 2:58 PM
>>>> To: [log in to unmask]
>>>> Subject: Re: [TN] BGA pad non-wetting
>>>>
>>>> Steve,
>>>>
>>>> I totally agree with John. My first thought was that the pad looked
>>>> like thin immersion tin where the IMC came to the surface an oxidized
>>>> in which case solder will not stick to the pad. But I don't know of
>>>> any BGA where they use Immersion tin so I still suspect you have an
>>>> ENIG Bad Pad issue.
>>>>
>>>> George
>>>>
>>>> -----Original Message-----
>>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
>>>> Sent: Thursday, December 21, 2017 2:51 PM
>>>> To: [log in to unmask]
>>>> Subject: Re: [TN] BGA pad non-wetting
>>>>
>>>> Assuming it's not ENIG???
>>>>
>>>> If not ENIG I would suspect immersion tin where the intermetallic has
>>>> come to the surface.
>>>>
>>>> If an ENIG problem or an immersion Tin problem it is not realistically
>>>> recoverable without impacting the assembly with some serious
>>>> reliability issues.
>>>>
>>>> Sent from my iPhone
>>>>
>>>> On Dec 21, 2017, at 11:39 AM, Steve Gregory <[log in to unmask]>
>>>>>
>>>> wrote:
>>>
>>>>
>>>>> Hi all,
>>>>>
>>>>> I've been asked to post this to the Technet by a dear friend:
>>>>>
>>>>> *We installed this little processor. At test we identified opens on
>>>>> the device. When we removed it we saw a number of pads that were
>>>>> matte gray with no evidence of solder adhered to the pad. * *We
>>>>> attempted to bump the pads with solder, they did not wet easily. In
>>>>> some cases we had to scrape through the matte finish to a shiny metal.
>>>>> But, we did get all the pads to appear wetted.*
>>>>>
>>>>> *We cleaned the site well and then fluxed the bumps with a tacky
>>>>> flux ROLO designed for POP, placed the BGA and reflowed it on a
>>>>> rework
>>>>> station.*
>>>>>
>>>>> *The assembly failed test with similar result, opens under the
>>>>> processor.*
>>>>>
>>>>> *The attached photo shows that the bump process only appeared to wet
>>>>> the pads. The condition returned when we removed the BGA second
>>>>> time.*
>>>>>
>>>>> *
>>>>> https://urldefense.proofpoint.com/v2/url?u=http-3A__stevezeva.homest
>>>>> ead.com_2017-2D12-2D21-5F11.21.17.jpg&d=DwIFaQ&c=nvOEfClv88r3To4eOyY
>>>>> tQN0213v_-JGWbujap2hCee4&r=-MAMt3MrjiRvYJiwVeFoas7eghr5IF6QpUBreyGR1
>>>>> qs&m=ZtT8m__jsmKXx-NxB6DAVryCAm8iznmmCFPq9PL_QqE&s=Du_vGyBf05tjpSvFe
>>>>> t5EPytyLuSbCfhNQ4wlPVTfIK8&e=
>>>>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__stevezeva.homes
>>>>> tead.com_2017-2D12-2D21-5F11.21.17.jpg&d=DwIFaQ&c=nvOEfClv88r3To4eOy
>>>>> YtQN0213v_-JGWbujap2hCee4&r=-MAMt3MrjiRvYJiwVeFoas7eghr5IF6QpUBreyGR
>>>>> 1qs&m=ZtT8m__jsmKXx-NxB6DAVryCAm8iznmmCFPq9PL_QqE&s=Du_vGyBf05tjpSvF
>>>>> et5EPytyLuSbCfhNQ4wlPVTfIK8&e= >*
>>>>>
>>>>> *Have you seen this before? Is there any recovery? This assembly is
>>>>> worth about $45K. *
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Steve
>>>>>
>>>>> --
>>>>> Steve Gregory
>>>>> Kimco Design and Manufacturing
>>>>> Process Engineer
>>>>> (208) 322-0500 Ext. -3133
>>>>>
>>>>> --
>>>>>
>>>>>
>>>>> This email and any attachments are only for use by the intended
>>>>> recipient(s) and may contain legally privileged, confidential,
>>>>> proprietary or otherwise private information. Any unauthorized use,
>>>>> reproduction, dissemination, distribution or other disclosure of the
>>>>> contents of this e-mail or its attachments is strictly prohibited.
>>>>> If you have received this email in error, please notify the sender
>>>>> immediately and delete the original.
>>>>>
>>>>
>>>>
>>>
>
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