Here is another example: a small FR-4 insulator was used under a metal-shell connector to prevent shorting to traces under the soldermask (did you know that soldermask is not considered an insulator?). The buyer found she could get the insulators .05 cheaper if she switched to a vendor who had the capability to laser cut the insulator and laser cut the holes in it for the connector leads. No qualification was performed (would you?). The old vendor milled out the insulator and drilled the holes. Awhile after the new insulators began to be used, they began having field failures in the device, and it was traced to what they thought was a solder short under the connector. They could not see anything causing the short in the X-rays, but it was difficult to see clearly. Upon removal of the connector, the short disappeared. Assumptions were made that the solder was pooling under the connector body, thus shorting the leads together or to the traces in tiny holes in the solder mask. As testing progressed, the short drew more and more current, eventually burning the assembly upon power-up.
Tests were made on the connector, on the via-to-via power handling capacity, etc. After three weeks of several engineers standing around scratching their heads over the cause of the short with returned goods piling up in the warehouse, one engineer noticed that on the replacement insulators there was a faint brown residue around all of the laser-cut edges. He thoughtfully set up a high-pot meter and measured the resistance of the outside edge of the insulator. The resistance was only 5K ohms.
As it turned out, the carbolization of the FR-4 from the laser cutting process created a low-resistance path from power to ground, and also from power to some of the signal lines. Because the holes were very close together, and also were very close to a window on the inside of the insulator, the carbolization provided a path for current. The more current that passed through, the more the carbolization increased, until there was nearly a dead short. Many of the devices were damaged from overstress. The customer insisted that none were reliable. It cost the company millions.
The moral of this, and many other similar stories, is:
Qualify every part and every material, every process, and every vendor.
If it ain't broke, don't fix it.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frederick Miller
Sent: Wednesday, August 17, 2005 8:50 AM
To: [log in to unmask]
Subject: Re: [TN] Ultrasonic Cleaning
The manufacturer of the edge board connector changed the US machine to one with a higher power level and did not do a requalification of the part. The higher energy caused the contact fingers to fatigue since they had no support. We had no hint of a problem until the field failures started to come in. It cost us over $ 20 million to find and replace the units in the field.
**************************
Frederick H. Miller PE
Astrolab, Inc.
4 Powder Horn Drive
Warren, NJ 07059
Tel: 732-560-3800
Fax: 732-560-9570
www.astrolab.com
[log in to unmask]
*****************************
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Burke
Sent: Tuesday, August 16, 2005 4:07 PM
To: [log in to unmask]
Subject: Re: [TN] Ultrasonic Cleaning
Think he actually says Assembled using ultrasonics, as in ultrasonic welding?
John
------------------------------------
Avanex
John Burke
Senior Manager RoHS Compliance
[log in to unmask]
40919 Encyclopedia Circle
Fremont
CA 94538
tel: 510 897 4250
fax: 510 979 0189
mobile: 510 676 6312
------------------------------------
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stadem, Richard
Sent: Tuesday, August 16, 2005 1:01 PM
To: [log in to unmask]
Subject: Re: [TN] Ultrasonic Cleaning
Hi, Fred
I am assuming you are talking about a connector that was ultrasonically attached, not cleaned ultrasonically?
Did you qualify the process?
If you are talking about a connector that was standard SMT, and you cleaned it using US, what was the fail mode? Broken contacts, solder fractures? I have never heard of a purely mechanical device being damaged by US. Not saying it could not happen, just wondering about the details so I can avoid this.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frederick Miller
Sent: Tuesday, August 16, 2005 2:40 PM
To: [log in to unmask]
Subject: Re: [TN] Ultrasonic Cleaning
We had a problem with a connector that was damaged when it was assembled using ultrasonics. The problem did not appear until after the system was in use by the customer. You need to know where the energy is going and if you are degrading the fatigue life of the internal assembly in any way.
**************************
Frederick H. Miller PE
Astrolab, Inc.
4 Powder Horn Drive
Warren, NJ 07059
Tel: 732-560-3800
Fax: 732-560-9570
www.astrolab.com
[log in to unmask]
*****************************
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
Sent: Saturday, August 13, 2005 3:24 AM
To: [log in to unmask]
Subject: Re: [TN] Ultrasonic Cleaning
Damage may occur in a few milliseconds. It depends on at least 10 factors, some of which are imponderable, such as where the nuclei are that trigger the cavitation.
Brian
David Tremmel wrote:
> Dear forum,
>
> I have some microBGAs which have a no-clean flux residue which must be
> removed before they can be reballed.
>
> I have been doing my homework regarding USC (ultrasonic cleaning) and
> would like opinions on whether or not putting the microBGAs in alcohol
> and putting them through a US cleaning cycle for 1 minute would damage
> the wirebonding.
>
> Most of what I see regarding USC is negative, but would only a minute
> be damaging to the parts or does the damage occur after more time
> (i.e. - 3 minutes, 5 minutes).
>
> As always, I appreciate the feedback.
>
>
> David
>
> P.S. - Ramon, you said a 15 minute soak in alcohol would do trick, right?
>
> _________________________________________________________________
> ¿Cuánto vale tu auto? Tips para mantener tu carro. ¡De todo en MSN
> Latino Autos! http://latino.msn.com/autos/
>
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