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Lead Free BGA Rework Process | Lead Free BGA Repair
Determining which assemblies are lead free and which are tin lead
Visual Differentiation
While experienced inspectors may be able to determine the aesthetic differences
between a lead-free PCB assembly and a tin-lead version, one cannot rely on the
“experienced eye”. “Less wetting out to the pad edges” (Figure A) and
“graininess and lack of shininess of the solder joint” (Figure B) are typical
comments about some lead-free solder joints. However, in cases where a Nitrogen
atmosphere was present during the reflow of the solder joint (Figure C), there
will be little visual differences between the lead free alloys and their
tin-lead counterparts.
Figure A- Example of less wetting out to the pad edges on a lead free device
Figure B- Example of grainy and dull surface finish of lead free BGA solder ball
Figure C- Example of solder ball where Nitrogen was used in the reflow
Analytical testing
There are several levels of testing that can be performed in order to confirm
the presence of any of the RoHS banned substances to confirm the make up of the
alloy of the BGA solder spheres. The lowest level of testing involves the use of
lead testing kits. These test kits use a simple swab on chemical in order to
detect the presence of elemental lead. A chemical reagent, which changes color
in the presence of lead, is swabbed onto the BGA balls to determine the presence
of lead (Figure D). Shortcomings of this method includes false readings as test
swabs can become contaminated and the shelf life of the reagent. XRF testing (IEC
62321) is a solid, non-destructive analytical approach to screening components
for the presence of lead, cadmium and mercury. It also detects elemental bromine
and chromium but will not be able to identify these compounds if they are in the
molecular form such as PBB or PBDE or the valent state of chromium. The XRF
handheld units (Figure E) can measure solder ball area but not sub-millimeter
solder bumps. These units will measure all elements in their field of view. A
solder joint on a PCB will have take an average reading of these elements of the
solder joint AND the PCB material. So there is an "averaging effect" which is
dependant on the field of view. There are also some benchtop designs of XRF
tools which provide smaller analysis areas. Many of these systems have X-Y stage
automation and mapping software which the XRF user can then use to map the
location of restricted metals on a device. These more sophisticated systems do
however come with a higher price tag.
Figure D- Swab on style reagent uses color to tell the user about the presence
of lead
Figure E- Handheld XRF tester provides good level of “first defense” in RoHS
compliance and due diligence
Marking of Boards and Parts
There are several industry guidelines which have been adopted by a portion of
the part vendors with respect to the marking of lead free components, boards and
assemblies. In May of 2004 JEDEC and the EIA adopted the JESD97 standard
(http://www.jedec.org/download/search/jesd97.pdf) which defines the marking and
labeling of lead-free components and assemblies. Similarly the IPC has released
the IPC-1066 defining the marking of same (http://www.ipc.org/TOC/IPC-1066.pdf).
Both of these standards provide specific labeling formats for PCB assemblies,
components and devices. In general these guidelines define the marking on a PCB
assembly (Figure F) to:
1. Be on the topside of the board, lower right hand segment
2. Contain information on the type of lead free alloy
3. Contain the maximum safe processing temperature
Figure F- Typical lead free component labeling scheme
Some vendors, though not all, have adopted a unique part numbering scheme for
their lead free parts.
Lead Free BGA Rework
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