| Gadget Review |  | |
We will once again be exhibiting at the MD&M Midwest show September 28 - 30 at the Convention Center in Rosemont IL.
If you need tickets, let me know, I still have some available.
We hope to see you there!
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BESTProto is now ITAR Registered and Compliant
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As part of an on-going effort to increase our ability to serve YOU, our customer, we continue to work on broadening our capability
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Featured Article
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We all love what surface tension does to solder to help
align parts such as BGAs now watch
how it works with a drop of water: http://www.flixxy.com/water-drop.htm
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Mixing Lead-Free and Tin-Lead Solder on a PCB Assembly
Summer is drawing to an end, the kids are back in school
and companies are getting back to business. Now is as good a time as any to talk about mixing lead-free (RoHS) solder with tin-lead solder (Sn63) paste on your PCB assemblies.
This situation arises most often when introducing a
lead-free BGA (Ball Grid Array) device with a PCB assembly that's being
processed using tin-lead solder.
Most all BGAs being produced today are being shipped with RoHS compliant
solder on them. Tin-lead solder balls
were probably phased out and not available on the current generation BGA device
and it's likely the previous generation came with RoHS solder balls as
well. Unless you've been able to strike
a deal with the device manufacturer by committing to buying very large
quantities, you're left holding the bag and trying to fend for yourself in
making these devices work in your application.
If you're like many of BESTProto's customer's in the
Medical, Military/Aerospace, and Industrial Equipment/Controls business, you're
not only exempt from RoHS compliance, your requirements for highly-reliable PCB
assemblies dictates you use tin-lead solder for your PCB assemblies.
There are a few ways to handle the issue of dissimilar
alloys:
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Switch the entire assembly to lead-free solder
Pros and Cons:
It would eliminate the issue of the dissimilar alloys however, since the reflow
temperatures of lead-free solder is about 30' C higher than that of tin-lead
solder, some of the other components on the board may not be able to withstand
the elevated temperatures needed for reflow.
- Reball the BGA with tin-lead solder and process
as a normal tin-lead assembly
Pros and Cons:
Reballing the BGA is one of your better options but there is additional cost
associated with the process and device manufacturers often discourage
subjecting the device to more than 3 heat excursions although studies conducted
by BESTProto sister company BEST Inc. show the devices to be more robust then
manufacturers are letting on.
-
Process the board with tin-lead solder and place
the RoHS BGAs using a BGA rework station.
Pros and Cons:
Since BGA rework stations use localized heat that's confined to the area of the
BGA device being placed; the entire board assembly isn't subjected to the additional
heat. Rework stations aren't cheap and
unless you can justify the cost and have a skilled person to run it often
enough to keep their skills sharp, you can have mixed results.
- Process the board with tin-lead solder with a
lead-free BGA
Pros and Cons: Although
this would seem to be the easiest solution, it's fraught with uncertainties. Since you'll end up with an unknown and untested
alloy, long term reliability is questionable. On the other hand, if you're just doing it to build prototypes, that may
not be a concern. Another potential
issue you may face is the phenomenon known as "Head-In-pillow" whereby the two
alloys don't actually bond to one another and you have a solder ball on the
device and a concave pad on the board which creates more of a spooning effect
and you have an open circuit.
Flux is an area you shouldn't overlook either because In
order to get the lead-free solder to go into reflow, you'd have to run the
entire board at the higher lead-free temperatures. The problem with doing that is the flux used in
the tin-lead solder paste wasn't designed for the higher temperatures and will
burn off prematurely leaving the solder joint unprotected and exposed to oxides
during the balance of the reflow cycle and may also cause a distorted solder joint
with voiding.
Another issue to be mindful of is that the PC board
itself may not have been produced with the ability to withstand the elevated temperatures. Most of the PCB fab houses require you tell
them if you need high temp capable substrates or key off the specified surface
finish to try and determine whether the board is to be processed as lead-free
or not.
The bottom line: if you're faced with having to place a
lead-free BGA onto a board that is primarily intended to be processed with tin-lead
solder paste. Consider reballing the BGA
with tin-lead solder balls or having it placed by an experienced technician
using a good quality rework station. Or,
you can always send it to BESTProto and we'll place it for you using the most appropriate
process for your specific application.
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 | "Garth's Garage" | Being a certifiable "gear head" most of my life, I have a passion for most things mechanical.
Whether its cars, motorcycles, bicycles or anything else with wheels
and/or an engine, it gets my engine racing. Since it's one of my favorite subjects, I've also done a fair amount of
reading on those subjects and have a host of otherwise useless knowledge that I
hope you find interesting and informative.
First Mass-Produced Fully Electric Car In U.S. the Nissan Leaf
Nissan will soon be releasing what is essentially the first mass-produced fully electric car called the "Leaf". Unlike the Toyota Prius or Honda Insight there is no gasoline (or any combustible fuel) engine. Even though the upcoming GM/Chevy Volt is primarily batter powered it has a gasoline engine that is used to regenerate the power in the batteries but it doesn't actually drive the wheels themselves.
Although GM made available a fully electric car the EV1back in 1996 to certain lease customers. Although you couldn't really call it mass-produced even though that was the intent at the outset. They eventually made about 800 and they weren't available for purchase, just leasing. GM pulled the plug (pun) in 1999 as profits were no where in sight.
The Nissan Leaf will be introduced in coastal states and Michigan initially but will be available country wide over time. If you're one of the fortunate ones, Nissan has a limited program for helping wire your home with a 240 volt A/C charger.
You can read more at http://www.motortrend.com/roadtests/alternative/1009_2011_nissan_leaf_second_opinion/index.html
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| Feedback and comments are always welcome. Please feel free to contact me any time
Sincerely,
Garth Cates
BESTProto Inc.
847-797-9250
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