Want a quartpound burger with french fries, no bread, Heinz ketchup,
french mustard, tartar sauce, boston mixture and a Czech beer.
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt
Sent: den 13 februari 2007 15:39
To: [log in to unmask]
Subject: Re: [TN] FW: Report from a BGA
Troubled Techies
If I might make an observation - I think you could avoid most of these
issues with Vapour Phase soldering.
Simple physics - a heated vapour at 225C will condense onto ALL surfaces
including under components and Hey Presto - uniform soldering. We have
many companies over here doing that even to the extent of doing away
with x-ray analysis.
Unless I am missing something?
Hope it helps
Kindest regards,
Graham Naisbitt
[log in to unmask]
On 12 Feb 2007, at 23:33, John Burke wrote:
> Yes I know the drill - it is a very small one..........8-)
>
> I have carried out that type of profiling many many times.
>
> I have found that the best type of drill to use is actually a dental
> drill and hand piece. What do other people use out of interest?
>
> John
>
>
>
> John Burke
>
> (408) 515 4992
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
> Sent: Monday, February 12, 2007 1:39 PM
> To: [log in to unmask]
> Subject: Re: [TN] FW: Report from a BGA
>
> We operate with the kind of knowledge that Richard and Werner have
> shared along with the experience of measuring many different kinds of
> assemblies, materials, with different methods of thermal transfer and
> tools.
> When we get
> the luxury of following the "correct" way of checking a board we also
> run thermal couples under parts, taped to the part, and taped to the
> board to learn how these materials respond to our machines and process
> methods. Then we make educated guesses, based on experience.
>
> You know the drill.
>
>
> Starting March 1, 2007 New Location
> Guy Ramsey
> R&D Assembly
> 1660 East Race Street
> Allentown PA 18109-9580
> (610) 264-1887
> FAX (610) 264-1877
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
> Sent: Monday, February 12, 2007 4:09 PM
> To: [log in to unmask]
> Subject: Re: [TN] FW: Report from a BGA
>
> What about us CEM's that rarely have the luxury of a spare bare board,
> or spare BGA's that we can play with?
>
> Sometimes we can convince our customers that we should have a spare
> PCB and BGA's to be able to properly set up a reflow profile, but most
> of the time we can't.
>
> What I do in that case, is to try and find a scrap PCB that might be
> close to the same thermal mass, and then I have some failed BGA's that
> have been pulled off a board from rework, and just lay them over top
> of my thermocouples, then do my plot.
>
> I know it's not exact, but it's the best I can do sometimes. I just
> try to ensure that I hit a high enough peak and stay liquidous for a
> decent amount of time.
>
> -Steve Gregory-
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Monday, February 12, 2007 2:56 PM
> To: [log in to unmask]
> Subject: Re: [TN] FW: Report from a BGA
>
> Werner, thank you for your note. I totally agree.
> I misread Inge's original email. I thought he said putting a
> thermocouple on top of the SOLDER PAD was misleading. What he actually
> said was putting a thermocouple on top of the component body was
> misleading. That is true.
> Another note. I totally agree the best way to thermocouple a profile
> test board is to drill up into the solder joint, insert the TC from
> the bottom so the weld is inside the solder ball. However, I then
> backfill the hole with thermally conductive epoxy with a minimum
> thermal conductivity of
> 14 BTU/in.
> hr. F. This helps reduce the insulative effect of the PWB just below
> the weld inside the hole. After the thermally conductive epoxy is
> cured, I then measure the electrical resistance of each of the
> thermocouple wires to the solderball via. I should get less than 1
> ohm. If I do, then I know that the weld is making full mechanical
> contact with the inside of the solderball and/or the pad. When the
> mole or data recorder runs through the reflow oven, and I see a very
> solid line on the graph, I know I am measuring the actual temperature
> of the solderball/pad mechanical junction. If the profile line is not
> a solid line throughout, but is "noisy" with little spikes in both
> directions, then I know I am only measuring air temperature under the
> BGA, and I disregard that particular reading. The attenuating effect
> of full metal contact is easily seen.
>
> Incidentially, I recently wanted to verify that a small bake oven was
> getting a particular subassembly up to a certain temperature in a
> pre-baking operation. When I suspended thermocouples around the
> component within the chamber (measuring the air temperature), the 4
> thermocouples measuring the air temperature consistently measured 6
> degrees C. less than the 5 thermocouples that I had embedded into the
> subassembly using the method I just described. This was long after all
> of the TC readings had flatlined.
> The calibration lab questioned as to how an object being warmed by the
> air currents inside the oven could be hotter than the air currents
> themselves.
> The only explanation I could offer is that the thermal transfer
> efficiency of air directly to a thermocouple weld is less efficient
> than a piece of metal heated by the air making direct contact with the
> weld. I proved this by taking the thermocouples measuring the air and
> switching them with the thermocouples measuring the subassembly. The
> measurements were exchanged, one for one. Again, the TCs measuring air
> were all exactly 6 or 7 degrees cooler than those embedded in the
> assembly. I then took one of the TCs measuring air and clamped it to
> the metal rack in the oven. It went up 6 degrees.
>
> The same phenomena holds true for a thermocouple weld sitting just
> above a BGA pad, measuring air temperature alone. I notice it always
> measures a few degrees cooler than a TC with a good mechanical
> attachment to the solder or the pad, even when the solder is in
> liquidus.
>
> ________________________________
>
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Monday, February 12, 2007 1:30 PM
> To: Stadem, Richard D.; [log in to unmask]
> Subject: Re: [TN] FW: Report from a BGA
>
>
> Hi Richard,
> Ingemar is absolutely correctthe only way you know what the t's are at
> the solder balls is to put thermocouples in them. It is indeed
> standar5d procedure see IPC-7530, 7.9.5.
> BGA solder balls get heated by conduction through the PCBmany people
> do not realize thisand BGA component body is in fact a heat sink and a
> shield preventing both convection and radiation heat transfer.
>
> Regards,
> Werner Engelmaier
> ?????
> Engelmaier Associates, L.C.
> Electronic Packaging, Interconnection and Reliability Consulting
> 7 Jasmine Run
> Ormond Beach, FL 32174 USA
> Phone: 386-437-8747, Cell: 386-316-5904 Werner Engelmaier
>
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