On Thu, 12 Nov 2015 12:20:53 -0600, "Robert L Wilson Jr."
wrote:
I was afraid that my rant was going to turn into a discussion on MFJ
quality or lack thereof. I was more interested in giving owners of
the various MFJ antenna analyzers a clue as to what might be wrong
with theirs, than attempting to fix the problem at the source. I'm
sure MFJ knows that they have a problem by now.
Wave soldering is a marginal thing, I think it is amazing how many times
it does work. Think about how it goes: Basically the PC board is
suspended just above a vat of molten solder, and a wave is caused to run
across the vat. The wave, we hope, just reaches up to the connections on
the board and solders them.
Nope. PCB's with surface mount devices are not wave soldered. I
worked for several companies that had wave solder machinery during the
1970's, before SMT parts were common. Keeping the production line
machinery going was one my side projects. These daze, components are
attached with solder paste and soldered using infrared or vapor phase
reflow ovens.
Please note that the MFJ-269 PCB's have all the components on the
component side and have no leaded components on the board (except for
some flex wires to the meter and battery and several ribbon cables).
Too high and it makes solder bridges.
Nope. Too low a temperature and you get bridging. The wave has to
touch the pads on the bottom of the PCB or the pads don't get
soldered. Too low a wave is a bigger problem, where the pads don't
get any solder.
Too
low and it either misses connections or at least does not stay on them
long enough.
Soldering time is controlled by the speed of the chain drive moving
the PAB across the wave, not by the height of the wave. There might
be a tiny variation in timing with height, but with the nearly
vertical sides of the wave caused by the weight of the solder, the
soldering time is about the same for all wave heights.
And it is not long on a connection at best, so does it get
it hot enough?
We had thermocouples stuck into the wave to control the temperature.
At worst, were off a few degrees one way or the other.
It is not just fairly inexpensive things like my MFJ analyzer that have
had problems. I did the "resolder the whole board" thing on my Phase
Linear preamp many years ago also, and that was by no means low end!
Bob Wilson
I'm still slightly mystified how the components looked like they were
properly soldered, while the solder didn't stick to the PCB pad. The
best I can offer is some grease on the pads. Also, it was only in one
part of the PCB (around the RF connector). The other half of the RF
board was just fine.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558