An MLCC flex crack starts when the board bends and a rigid termination transfers that
strain into the brittle ceramic body. Walsin Technology (Walsin) qualifies general purpose
MLCCs to 1 mm of substrate deflection. The soft termination SH, SG and ST series are
qualified to 5 mm. That one number, printed in every datasheet, is what soft termination
buys.
What is an MLCC flex crack?
A flex crack is a fracture through the ceramic dielectric caused by mechanical strain, not
by heat or voltage. The board bends, the solder joints hold the terminations still, and the
difference has to go somewhere. It goes into the ceramic, which has almost no tensile
strain capability.
A flex crack rarely opens the circuit. It creates a conductive path through the dielectric that starts as degraded insulation resistance and
grows under bias. The board passes in-circuit test, passes functional test, ships, and fails
weeks or months later as a partial or full short.
Walsin’s application guide is blunt. Capacitors cracked by dropping or bending the board may cause deterioration of the insulation resistance and
result in a short, and the guide asks designers to add a fail-safe such as a fuse where a
shorted capacitor could cause an electric shock, smoke or fire. That instruction sits in
the MLCC Application Guide, section 5-2-3.
How much board bend does a standard Walsin MLCC survive?
One millimetre. Walsin’s general purpose MLCC datasheet specifies a bending test in which a
pressurising rod deflects the middle of the substrate at about 1 mm per second until
deflection reaches 1 mm, held for 5 plus or minus 1 second. X7R and X5R parts must stay
within 12.5% capacitance change.
That 1 mm figure is the baseline for the whole catalogue, and easy to exceed without noticing.
A 1.6 mm FR4 panel snapped apart by hand at a mouse-bite is not being bent 1 mm. Neither is a
board pressed onto a bed-of-nails fixture with the pin pressure turned up to cure an
intermittent contact, which the application guide names as a crack cause.
The MG series is the trap. MG is Walsin’s high-reliability, non-AEC-Q200 automotive
and industrial line, and the name implies a tougher part. Its
bending test
is the same 1 mm deflection as general purpose. Higher reliability grading and higher bend
capability are separate properties.
How far apart are the Walsin series on the bend test?
Five times, from end to end. General purpose and MG sit at 1 mm. AEC-Q200 MT is tested to
3 mm, tightened to 2 mm for X7R. The soft termination SH, SG and ST series are tested to
5 mm. ST also holds the deflection twelve times longer than SH and SG do.
| Walsin series | Example part from our data | Bend test deflection | Hold time | Test clause | Match / mismatch vs general purpose |
|---|---|---|---|---|---|
| General Purpose | 0805B103K500 |
1 mm | 5 ±1 s | Bending Test, item 10 | reference |
| MG high reliability | MG21B103K500 |
1 mm | 5 ±1 s | Bending Test, item 10 | match: deflection, hold time · mismatch: none on bend |
| MT, AEC-Q200 | MT21B103K500 |
3 mm, 2 mm for X7R | 60 ±1 s | Board Flex, AEC-Q200-005 | mismatch: 2× deflection at X7R, 12× hold time |
| SH soft term, Ag-poly | SH21B103K500 |
5 mm | 5 ±1 s | Bending Test, item 10 | match: hold time · mismatch: 5× deflection |
| SG soft term, Cu-poly | SG21B103K500 |
5 mm | 5 ±1 s | Bending Test, item 10 | match: hold time · mismatch: 5× deflection, Cu-polymer |
| ST soft term, AEC-Q200 | ST21B103K500 |
5 mm | 60 ±1 s | Board Flex, AEC-Q200-005 | mismatch: 5× deflection, 12× hold time, AEC-Q200 |
Sources, in order:
General Purpose,
MG,
MT,
SH,
SG,
ST.
Every part number in the table returns a row in Walsin’s own parametric export, and all six
are 0805, X7R, 10 nF, 50 Vdc.
The pass criterion is identical across all six: X7R within 12.5% capacitance change, NP0
within 5% or 0.5 pF, whichever is larger, and no remarkable damage. Only the deflection and
the hold time move.
What does the soft termination layer actually change?
It inserts a compliant conductive polymer between the ceramic and the outer metal
termination. Strain arriving from the solder joint is taken up in the polymer rather than
being handed to the dielectric. Walsin describes the layer as absorbing mechanical stress
caused by PCB handling in the SMT line.
Nothing else changes. The dielectric is the same class, the capacitance and voltage are the
same, and the reflow profile is the same six numbers Walsin publishes for the whole MLCC
range. Soft termination is a mechanical fix for a mechanical failure mode: it does nothing for
DC bias loss, temperature coefficient or ageing.
SH uses a silver-polymer termination, coded C for
Ag Polymer in the SH ordering key. SG uses copper-polymer, coded C for Cu Polymer in the
SG ordering key. Both are qualified to the same 5 mm.
Which Walsin soft termination series has the part I need?
Almost certainly SH. Venatech Limited, an authorised Walsin distributor in Hong Kong, holds
an extract of 24,026 Walsin MLCC part numbers. Soft termination coverage inside it is
extremely uneven: SH has 1,524 parts across ten case sizes, ST has 118 across eight, SG has
65 across four, and VT returns nothing.
| Series | Parts held | Case sizes | Dielectrics held | Voltage span held | Match / mismatch on coverage |
|---|---|---|---|---|---|
| SH, Ag-poly | 1,524 | 0402, 0603, 0805, 1206, 1210, 1808, 1812, 1825, 2220, 2225 | X7R 1,046 · NP0 450 · X5R 27 · X7T 2 | 6.3 Vdc to 3000 Vdc | reference |
| ST, AEC-Q200 | 118 | 0402, 0603, 0805, 1206, 1210, 1812, 1825, 2220 | X7R 115 · NP0 3 | narrower | match: 5 mm bend · mismatch: 7.7% of SH’s part count, no X5R, no X7T |
| SG, Cu-poly | 65 | 0603, 0805, 1206, 1812 | X7R 55 · NP0 10 | narrower | match: 5 mm bend · mismatch: 4.3% of SH’s count, four sizes only |
| VT, VW80808 | 0 in the parametric data | none returned | none returned | none returned | mismatch: datasheet only, no orderable data |
Unique to Venatech’s data. Soft termination coverage in Walsin’s catalogue is wildly
uneven. SH holds 1,524 parts across ten case sizes, ST 118 across eight, SG 65 across
four, and VT returns zero rows from Walsin’s own parametric search despite having a full
21-page datasheet. Measured from our extract of Walsin’s export; not published anywhere.
Two further things our extract shows. First, SH55B475K101 —
a 2220 X7R 4700 nF 100 Vdc part carrying the SH soft-termination prefix — is filed in
Walsin’s export under “Big sizes Caps 1825 2220 2225”, not under the SH series. Search by
part-number prefix and you get 1,525 SH parts. Filter by series name and you get 1,524. One
real soft-termination part is invisible to the series filter.
Second, the X7T dielectric appears exactly twice in the whole 24,026-row extract, and both
occurrences are SH 2220 parts: SH55T225K251 and SH55T225M251, 2200 nF at 250 Vdc. If a
specification calls for X7T from Walsin, those two parts are the entire offering.
Can I drop a soft termination part into the same footprint?
Not without checking thickness. All six 0805 X7R 10 nF 50 Vdc parts in our comparison share
the same 2.00 mm length and 1.25 mm width. The general purpose, MG and MT parts are 0.80 mm
thick. The SH, SG and ST parts are 1.25 mm thick. That is a 56% height increase in the same
outline.
| Part number | Series | L (mm) | W (mm) | T (mm) | Match / mismatch vs 0805B103K500 |
|---|---|---|---|---|---|
0805B103K500 |
General Purpose | 2.00 ±0.15 | 1.25 ±0.10 | 0.80 ±0.10 | reference |
MG21B103K500 |
MG | 2.00 ±0.15 | 1.25 ±0.10 | 0.80 ±0.10 | match: all three dimensions and tolerances |
MT21B103K500 |
MT, AEC-Q200 | 2.00 ±0.15 | 1.25 ±0.10 | 0.80 ±0.10 | match: all three dimensions and tolerances |
SH21B103K500 |
SH, Ag-poly | 2.00 ±0.20 | 1.25 ±0.10 | 1.25 ±0.10 | match: nominal L, W · mismatch: 1.25 mm thick, wider L tolerance |
SG21B103K500 |
SG, Cu-poly | 2.00 ±0.20 | 1.25 ±0.10 | 1.25 ±0.10 | match: nominal L, W · mismatch: 1.25 mm thick, wider L tolerance |
ST21B103K500 |
ST, AEC-Q200 | 2.00 ±0.20 | 1.25 ±0.10 | 1.25 ±0.10 | match: nominal L, W · mismatch: 1.25 mm thick, wider L tolerance |
Height matters under a shield can, a heatsink or a mating board, and for wave soldering,
which Walsin permits for 0603, 0805 and 1206 only below 1 mm. Every soft-termination part in
that table is above the line. The land pattern does not change — the 0805 reflow footprint in
Walsin’s application guide is the one you already have.
What on my line is cracking the capacitors?
Usually depanelling, test-fixture pressure or placement head height, in that order. Walsin
names all three. The guide asks that the board is not bent or distorted after soldering in
handling and storage, that functional-test check pins are adjusted so they do not bend the
board, and that boards are not piled up after mounting.
Fix the process before changing the part. Route the panel so the break line
runs parallel to, not across, the long axis of large capacitors, and keep large case sizes
away from break lines and mounting holes. Support the board under the test fixture. Check
the placement head bottom dead centre and the centering jaw wear, which Walsin calls out as a
crack cause.
Change the part when the strain is structural and cannot be designed out: press-fit
connectors, screw-down modules, large boards with widely spaced mounting points, anything
that sees vibration or drop in service. That is where 5 mm of qualified deflection is worth
the extra 0.45 mm of height and the narrower part range.
FAQ
What is an MLCC flex crack?
A flex crack is a fracture through the ceramic dielectric caused by board bending rather than by heat or voltage. It usually degrades insulation resistance instead of opening the circuit, so the board passes electrical test and fails later in the field as a partial or full short. Walsin asks for a fail-safe where that matters.
How much board bend can a standard Walsin MLCC take?
Walsin’s general purpose MLCC datasheet specifies a bending test to 1 mm of substrate deflection, applied at about 1 mm per second and held for 5 plus or minus 1 second, with X7R and X5R staying within 12.5% capacitance change. The MG high-reliability series specifies the same 1 mm deflection.
How much bend does a Walsin soft termination MLCC take?
Five millimetres. The SH, SG and ST datasheets all specify a bend test to 5 mm of deflection. SH and SG hold the deflection for 5 plus or minus 1 second under the standard bending test clause. ST holds it for 60 plus or minus 1 second under AEC-Q200-005 Board Flex.
Is an AEC-Q200 MLCC already protected against flex cracks?
Only partly. Walsin’s AEC-Q200 MT series is tested to 3 mm of deflection, tightened to 2 mm for X7R, held for 60 plus or minus 1 second. That is better than the 1 mm general purpose figure and well short of the 5 mm the soft termination series reach. AEC-Q200 and soft termination are separate qualifications.
Does the MG series have better bend performance than general purpose?
No. The MG datasheet specifies the same 1 mm bending test as the general purpose datasheet, with the same pass limits. MG is graded for reliability in non-safety automotive and industrial equipment, which is a different property from bend capability. Do not assume the higher-grade name buys mechanical margin.
Which Walsin soft termination series has the widest range?
SH, by a wide margin. Venatech’s extract of Walsin’s parametric export holds 1,524 SH parts across ten case sizes from 0402 to 2225 and 6.3 Vdc to 3000 Vdc, against 118 ST parts, 65 SG parts and zero VT parts. If a board simply needs soft termination, start in SH.
Is a soft termination MLCC the same height as the standard part?
Often not. All six 0805 X7R 10 nF 50 Vdc parts we compared share a 2.00 by 1.25 mm outline, but the general purpose, MG and MT parts are 0.80 mm thick while the SH, SG and ST parts are 1.25 mm thick. Check the height budget and the wave soldering limit before swapping.
Does soft termination change the reflow profile or the land pattern?
No. Walsin publishes one reflow profile for its MLCC range, and the application guide’s land patterns are per case size, not per series. Soft termination addresses mechanical strain only. If the parts are cracking in the oven rather than on the panel, the profile is what needs attention.
Next step
Flex cracking is a selection problem with one number in it. Send the BOM lines that sit near
break lines, connectors or mounting points, and Venatech Limited, an authorised Walsin
distributor in Hong Kong, will return the qualified bend deflection for each part, the soft
termination options that match the value and voltage, and the thickness difference you would
be designing in.
Send your BOM to Venatech · Browse the
Walsin MLCC range · Read
Soft termination MLCC: SH, SG, ST and VT and
MLCC reflow profile and mounting.
Cross it yourself. The cross-reference tool takes a single part number or a whole BOM column and returns the Walsin candidates with every field that differs stated plainly — qualification stays with you. Ready stock shows what is held in Hong Kong today, with an RFQ against any line.