User's Manual

Page 49
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The set shows typical X-Ray images of sample modules soldered to an assumed application
board including some failure samples. The images are taken from assembly and BLR testing
and comprise two different stencil versions (110μm and 150μm thickness).
A good solder joint at Frey M1 signal pins in X-Ray inspection is characterized by a
rectangular shape, described by the dimensions of the pad at the module.
Solder joints which have a round footprint in X-Ray image are found in areas with high stand
off and are more column like instead of flat. These are good from electrical point of view but
indicate processing problems like aslope standing of the module or warpage.
It is recommended to use X-Ray to determine level of voiding. Entrapments of gases can
often not be completely avoided, if large flat solder joints are used. Currently there are no
standards available defining limits for void content. The available IPC610 standard for ball
grid arrays (=BGA) must not be applied to LGAs and hence to the Frey M1 SMT modules.
As seen from the X-Ray images above there is no significant difference in reflow result for the
110μm and 150μm stencils. This is mainly due to the fact, that the resulting volume was kept
constant by varying the apertures accordingly. The resulting shape of the solder joint is only
influenced by the volume.
Only if solder paste spreading is limited, which can occur with lead free solder on Cu-OSP or
immersion tin PCB surfaces, a little difference in solder joint shape can be expected but with
no effect on quality or yield. This is a characteristic of lead free solders and not a wetting
issue.
4.5. Board Level Reliability Investigation
The board level reliability tests described as follow table
Item No
Test case
International standard
1
Storage Test
IEC60068-2-1
IEC60068-2-2
2
Thermal Cycle
IEC60068-2-3
IEC60068-2-56
IEC60068-2-38
IEC60068-2-30
3
Thermal Stress
IEC60068-2-3