-----Original Message-----
From: Roger M. Stoops [mailto:[log in to unmask]]
Sent: Monday, August 27, 2001 10:38 PM
To: [log in to unmask]
Subject: [TN] SMD Assembly Problems
Esteemed Colleagues,
An engineer here wants to reject some SMD assemblies that were assembled by
hand. I have reviewed the A-610, but it doesn't necessarily cover all the
problems we see. The product has been exhibiting random field failures,
and some are failing at temperature extremes (-20deg C or +70 to 85deg C).
1) Some pads are missing under a MQPF-144 device. "Former" pads with a
connection have the lead raised off the board and wire soldered from lead
to a via under the device. Some unconnected pads are missing and no solder
joint is possible. Accept or reject?
Reject - not sure what damaged may have been incurred while altering the
lead, and coupled with a missing pad/wire mods is a concern.
2) On same device, the wire fix for the removed pad raises the device so
that the leads had to be bent to the board and then soldered. Looks bad.
Accept or reject?
Reject - mechanical stresses and strains to devices is bad news. Considering
that this is unusual practice, operators do not understand what is good, bad
or indifferent. No one is trained to do mods of this nature. Reject, reject.
3) What are your thoughts about manual SMD assembly with fine pitch parts
down to 0.5mm for production? (By manual I mean manual part placement and
manual soldering.)
If this is production and volumes - forget it, you are courting disaster. It
can be done by an exceptionally diligent operator, the time required to
solder these devices itself introduces quality/reliability concerns.
4) What are your suggestions as to having our CM improve their soldering
techniques?
Training, training, ad infinitum is the only way out AND continually
assessed - all our operators have been trained and are continually assessed
on the job. Our process engineers train and educate our operators on a
continuous basis, most especially due to varying customer requirements, new
devices, designs etc.
Sorry I don't have pictures for Steve-o's web site. Something I will have
to work on for the future. We rarely have problems from our CMs (congrats
to the CMs out there...).
Big TIA,
Roger M. Stoops, C.I.D., PCB Designer
Trimble
Engineering and Construction Division
5475 Kellenburger Rd.
Dayton, OH 45424-1099 USA
Ph: +01 937.233.8921 or +01 937.233.4574 ext 288
Fax: +01 937.233.7511
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