A slight aside.
I got summoned to a customer who was investigating a low yield on a new RF product that we were manufacturing.
On some of the FETs the customer had been able to pry off the Drain and source legs by lifting the toe and then rolling up the leg and this showed that there was some voiding under the leg which he claimed shouldn't be there and the voids produced a poor mechanical and a poor RF joint.
I was unable to convince him that his test was invalid, that voids did exists, but the joints were unable to resist his rolling up test.
Fortunately we made lots of older products for this customer using the same devices on the same style of pcbs which had acceptable RF yields.
He did finally accept that there were other possible problems leading to the low yields.
Irony always has to be used with care with a customer, I suppose admitting that the product also fails the hammer and chisel test isn't a good idea.
Regards
Rex
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: 28 November 2011 13:13
To: [log in to unmask]
Subject: Re: [TN] Mechanical testing of joints
Hi Ioan - what you describe is not a test, it is someone playing around with a screwdriver. The failure location of a solder joint is a combination of many factors - Andy just touched the top of the list of things that need to be characterized and documented. Force on solder joints do not always result in the pwb pad being the failure location. If someone wants to test the solder joint strength, then they should put the screwdriver down and conduct a test with the appropriate equipment.
Dave
Ioan Tempea <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
11/24/2011 09:21 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Ioan Tempea <[log in to unmask]>
To
<[log in to unmask]>
cc
Subject
Re: [TN] Mechanical testing of joints
Hi Andy,
The test was simply like that: somebody took a screwdriver and manually
applied a force until something broke. No control, no aging, nothing else
and, on top of it, I did not see the tested samples yet, so I have no clue
whether the separation is interfacial part-solder or in the solder. The
main reason was that the end caps of the fuse are gold plated and the
solder (SAC305) doesn't go uphill much.
Based on the assumption that a good joint means pads will lift before
anything else yielded, this screwdriver test came up and it turns out the
lands did not lift, but the component came off, I believe (seeing a couple
of pictures) with some solder on it, which rather points to failure in the
solder.
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask]
W | www.digico.cc
N'imprimer que si nécessaire - Print only if you must
-----Message d'origine-----
De : Giamis, Andy [mailto:[log in to unmask]]
Envoyé : November-24-11 10:10 AM
À : TechNet E-Mail Forum; Ioan Tempea
Objet : RE: Mechanical testing of joints
Hello Ioan
How much force was applied? How was the force applied (tensile, shear,
etc)?
Was it less force than you expected? (How much less?)
How did the solder wetting appear before the test?
Were there any other test factors, such as aging?
What was the solder?
Did the component actually break or was it a solder / intermetallic
failure?
My first thoughts are that if you apply enough force, sooner or later,
something is going to break.
If the pads are really well-designed and firmly anchored into a well-built
board, the pads may tolerate more force than you'd expect.
________________________________________
From: TechNet [[log in to unmask]] On Behalf Of Ioan Tempea
[[log in to unmask]]
Sent: Thursday, November 24, 2011 9:40 AM
To: [log in to unmask]
Subject: [TN] Mechanical testing of joints
Dear Technos,
Force was applied to an SMT passive part, just to see when and how it will
break. It happened that it broke on the component side, rather than
tearing the pad apart. And now we have a controversy, some say the
soldering was not good, since the pad should always lift before ripping
the component. Is it true, or the damage can occur just anywhere depending
on so many factors, like the footprint, size of part (we're talking here
of a rather thick part, 2.7 mm)?
See the part here
http://www.littelfuse.com/searchresults.html?NttP=0451002.MRL&Ntt=0451002.MRL
So, again, is it the pads that should always rip under mechanical shock,
or just anything in the joint could break?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] <mailto:[log in to unmask]>
W | www.digico.cc <http://www.digico.cc/>
N'imprimer que si nécessaire - Print only if you must
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