Dave,
Non-metallic coatings do not stop tin whisker growth...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave He
Sent: Monday, February 15, 2010 5:43 PM
To: [log in to unmask]
Subject: Re: [TN] Pre-Tinned BGA? - Found word(s) to be removed list error remove list risk free in the Text body
Some customers don't allow the BGA to be reflowed more than twice. If this
is applied to your product, you can only reflow it once after re-ball.
Underfill is not the solution for tin whisker. But some coating (XY) will
help stop tin whisker growing.
Regards,
Dave He
Ext: 333
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Monday, February 15, 2010 4:27 PM
To: [log in to unmask]
Subject: Re: [TN] Pre-Tinned BGA?
Agreed. 1 or 3 but no other.
Rich Stadem posted this helpful advice on reballing BGAs:
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, October 07, 2009 11:34 AM
To: [log in to unmask]
Subject: Re: [LF] Quality/Reliability of 're-balled' BGA devices
I have seen literally hundreds of thousands of BGAs reballed many I
performed myself, with both convection methods as well as using a
proprietary laser ball attachment process. I was the engineer for these
processes either at companies I have worked for in the past, or with
companies I currently work for (I am a consulting engineer for several
companies as well as being an employee of GD).
If done properly using a controlled method, such as the paper pre-forms from
Six Sigma/Winslow Automation or with solder spheres poured into the
appropriate stencil, in conjunction with a set convection reflow profile,
along with an automated ball removal method (not a hot-air vacuum method,
however) I have never seen a BGA fail prematurely because it was re-balled.
I have seen many fail because the process was not controlled, however. When
critical steps such as pre-bake are skipped the components will not survive,
or their reliability will be reduced.
Use of the wrong fluxes, improper rework methods, improper reflow profiles,
etc. can also cause issues.
I have twice captured field reliability data from BGAs that were re-balled,
both with BGAs reballed using convection and with those re-balled using
laser. Both were instances where a number of BGAs needed to be removed,
re-balled, and replaced. The first instance was to put the parts on a
different PWB, the second instance was to change the alloy from Sn63 to
Kester K100DL, but not to meet RoHS requirements.
In both instances, the re-balled BGAs had longer mean times before failure
than the BGAs that were never re-balled. While I am not absolutely certain
as to why, I believe it is because the SJs on the re-balled BGAs were
superior due to the fact that new balls were added to the BGA pads that had
been essentially pre-tinned during the removal of the original solder balls
and the site prep performed on the BGA pads.
While working for Analog Technologies in Burnsville, Mn, we developed a
laser soldering machine as well as a process for performing laser ball
attachment using a proprietary oxygen evacuation chemical process (read
about it here www.analog-tech.com). This process removes all oxygen from
around the ball during the laser soldering (no nitrogen is used) leaving
behind perfectly pristine solder balls with no wetting issues. This process
also does not heat up the BGA, CSP, or flip chip itself, because all of the
energy is focused on the solder ball and the pad. This eliminates two of the
four heat cycles necessary to remove a BGA, strip the old solder, reball,
and reattach it.
Analog has been performing BGA original ball attachment and re-balling for
several years now, and we have not seen any, repeat, no issues with BGAs
that were either reballed or attached with laser or controlled convection
processes.
BGA rework and reballing is generally a safe procedure, but only as long as
the process is qualified and controlled. All too often I have been called in
to look at rework processes where it is done with a different method each
time depending on which operator did it, what day of the week it was done,
and how the constellations were aligned. The results were to be expected
including delamination of the die, delamination of the BGA substrate,
popcorning, and other issues.
====================
Bob Landman
H&L
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Monday, February 15, 2010 6:31 PM
To: [log in to unmask]
Subject: Re: [TN] Pre-Tinned BGA?
(3) And (1). But not the other. (3) required nothing to be done on the
assembly level. All the rel data are valid. (1) may need reduced rel qual.
The others, as material change, most of the mil or hi rel house need full
qual (shake, drop all the nine yard). It would cost around 30 to 50k plus
risk budget (depend upon how complicated is your assembly) and 3 month
delay. At least it use to be. My ancient 1.8 cents.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Feb 15 17:49:57 2010
Subject: [TN] Pre-Tinned BGA?
Hello All,
I had a question to see if anyone has tried anything different. Most of our
customers are some how related to the military. So we have one product that
the customer just found out was a PB-Free device. They want us to "pre-tin"
the spheres. Now I have tried several process for forward and backward
processes. None of them include re-tinning of a BGA Device. We do re-tin
other leaded and some non leaded devices. So below are the three options I
have recommended but still have reliability concerns as the end product is
to be coated with Paralyne.
1. Re- Ball to PB/SN
2. Sue a selective rework machine and place pate with isolated heat if the
substraight could handle.
3. Purchase the component in PB/SN material 4. Reflow the product with
slightly higher temps (5c per 10 zones) once out of over and cold to room
temp underfil the device.
Again if anyone has any more ideas I am game!!
Carl Ray
Lewisburg TN 37091
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