Design-In Support: From Part Selection to Mass Production

Design-in support runs six stages: part selection, cross-reference, qualification, FAE
assistance, AEC-Q200 support and mass production. Each stage answers a different question
against real manufacturer data, and each one has a characteristic failure. The stages that
catch most are part selection, where the manufacturer’s own search tool hides real parts, and
qualification, where the published number is the wrong number.

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds parametric data for
359,974 Walsin Technology (Walsin) part numbers across eight product lines. Every figure
below is measured against that extract.

---

What does design-in support actually cover?

Six named stages, in sequence, each with its own output. Part selection narrows the catalogue
to candidates. Cross-reference moves an existing line field by field. Qualification checks
the numbers a datasheet table does not publish. FAE assistance resolves the BOM. AEC-Q200
support confirms status. Mass production fixes packaging and traceability.

The sequence matters because a failure caught late costs a board spin and a failure caught
early costs a message.

How do I select a part the manufacturer’s own search tool hides?

Ask someone who holds the extract rather than trusting the filter dropdown. 3,615 Walsin
chip resistors sit at rated powers that do not appear in Walsin’s own filter menu — 1,950
parts at 1.5 W and 1,665 at 1/5 W. They are real, orderable parts, and they are invisible
to anyone selecting from the public search tool.

Both groups live in a single case size each. All 1,950 of the 1.5 W parts are 2010. All 1,665
of the 1/5 W parts are 0402. If you are trying to get 1.5 W out of a 2010 pad, or 200 mW out
of an 0402 pad, the parts exist and the filter will not show them to you.

Part number	Case size	Resistance	Tolerance	TCR	Rated power	Match / mismatch against Walsin’s public filter dropdown
WF20A1R00FTL	2010 (5025)	1.00 Ω	±1%	≦±100 ppm/°C	1.5 W	Mismatch — 1.5 W is absent from the dropdown. One of 1,950 such parts
WF04P1024FTL	0402 (1005)	1,020,000 Ω	±1%	≦±100 ppm/°C	1/5 W	Mismatch — 1/5 W is absent from the dropdown. One of 1,665 such parts
WF08A1002FTL	0805 (2012)	10,000 Ω	±1%	≦±100 ppm/°C	1/2 W	Match — 1/2 W is in the dropdown and the part is findable
WF06B4R99TTL	0603 (1608)	4.99 Ω	±0.01%	≦±3 ppm/°C	1/10 W	Match on the filter · mismatch if the design needs thick film rather than thin film

Unique to Venatech’s data. 3,615 Walsin chip resistor part numbers sit at rated powers
missing from Walsin’s own parametric filter dropdown: 1,950 at 1.5 W, all in 2010, and
1,665 at 1/5 W, all in 0402. Two independent counts of the current extract agree on both
figures. Nobody selecting from the public search tool will ever see them.

How does a cross-reference work without the word equivalent?

By printing both sides field by field and marking each field as a match or a mismatch. Never
by declaring a part a substitute. Capacitance, tolerance, rated voltage, dielectric, case
size, thickness, termination and qualification status each get a verdict, and thickness and
termination are where crosses actually fail.

Bring the part number you already have. We bring the Walsin side from our own data, with the
datasheet reference behind each field, and flag our own gaps rather than filling them with an
assumption. The method is set out in
How to cross-reference an MLCC properly.

One rule holds across every cross we run. We never state that any other manufacturer’s part
number is discontinued, obsolete or constrained, because we do not hold anyone else’s affected
part list. Confirm status with the original manufacturer, and confirm the cross against both
datasheets before you qualify it.

What does qualification check that a datasheet table does not?

The number the parametric table leaves out. For a switching regulator, the number that
matters is saturation current, and only 146 of the 5,410 Walsin inductors in our extract
publish one. The other 5,264 give rated current alone, which is a thermal figure, not a
magnetic one, and it is the wrong number for a buck converter.

Rated current tells you how much current the part can carry before it gets too hot.
Saturation current tells you where the core stops behaving like an inductor. In a switching
converter the second limit usually arrives first, and it can arrive a long way first.

Part number	Series	Size	Inductance	RDC	Rated current	Saturation current	Match / mismatch for a 500 mA buck converter
MIP1608H2R2MBP	MIP-H	1608 (0603)	2.2 µH ±20%	0.20 Ω	600 mA	230 mA	Match on rated current · mismatch on saturation — the core saturates at 230 mA
MIP1608H4R7MBP	MIP-H	1608 (0603)	4.7 µH ±20%	0.44 Ω	600 mA	60 mA	Match on rated current · severe mismatch — saturation is a tenth of the rated figure
MIP2012H2R2MBE	MIP-H	2012 (0805)	2.2 µH ±20%	0.17 Ω	900 mA	550 mA	Match on both figures — the only line here that clears 500 mA on saturation
WLPH252012M2R2PP	WLPH	2520	2.2 µH ±20%	85 mΩ	2.27 A	not published	Match on rated current · mismatch on evidence — no saturation figure exists to check

MIP1608H4R7MBP is the worked example to keep. Rated current 600 mA, saturation current
60 mA. A designer who sized a 500 mA converter on the rated figure has chosen a part that
leaves saturation before it reaches half the target current, and the datasheet table they
read did not lie — they read the wrong column.

Unique to Venatech’s data. Only 146 of 5,410 Walsin inductors publish a saturation
current. Narrowing to the 644 microhenry-class parts, the ones a switching converter would
actually use, 498 still publish none. The three series that do are CSME, CSMEA and MIP-H.
The background is in
Rated current vs saturation current in chip inductors.

Where does AEC-Q200 support fit into the sequence?

Immediately after part selection and before any layout commitment, because qualification
status is the one field that cannot be designed around later. Walsin writes the status into
the MLCC series name itself, so the check is readable rather than inferred, and it separates
part numbers that are otherwise identical.

Two Walsin automotive MLCC families differ by a single character in the part number. The MT
series is stated as qualified to AEC-Q200. The MG series is stated as automotive without
AEC-Q200 certification. MT21B104K500 and MG21B104K500 are both 0805, X7R, 100 nF, 50 Vdc
and 0.80 mm thick. Only one of them passes an automotive audit.

The practical instruction is short. Tell us at the selection stage whether the programme
requires AEC-Q200, and the candidate list changes before anyone draws a footprint. Told
afterwards, the same information becomes a change request.

What changes when the design moves to mass production?

Three things stop being specifications and start being logistics: packaging quantity, date
code traceability, and whether a line needs protecting. A part that was a datasheet entry
becomes a reel with an increment, a receipt date and a position in a stock file.

Packaging quantity is the one that surprises engineers. In the 23 September 2026 Venatech
stock snapshot, standard packaging quantity tracks case size closely: 15,000 at 0201, 10,000
at 0402, 4,000 at 0603 on the MLCC lines, and 5,000 at 0603 on the chip resistor lines.
0402B104K500 is held at an SPQ of 10,000, so a 12,000-piece requirement is two reels rather
than one and a bit.

Traceability is the second. Every line is supplied through the authorised channel, in original
manufacturer packaging, sealed, with full lot and date code traceability, and a Certificate of
Conformity available on request. Walsin’s MLCC application guide states the products should be
used within 12 months upon receipt, so the date code on the reel starts your own use-by clock.

The third is buffer stock, held on long lead-time part numbers for contracted accounts. That
is a commercial arrangement rather than a technical one, and it is agreed per part number
rather than offered as a blanket. The procedure for checking and reserving a specific line is
in How to check Walsin stock and reserve it.

Note. The cross-reference tool, ready stock and
the BOM and RFQ basket are live, so the selection and cross stages can start
without us. Quotation and qualification still run through a person, and that is deliberate:
a cross result is a candidate, not an approval.

What should I send at each stage?

At selection, the electrical requirement and the physical constraints: value, tolerance,
voltage or current, the height ceiling in millimetres, the dissipation, and whether AEC-Q200
is required. At cross-reference, the incumbent part numbers. At mass production, the annual
volume and the on-site dates.

The single most useful thing you can add at any stage is the constraint you think is obvious.
Height ceilings, saturation current targets and qualification requirements are the three that
most often go unsaid and most often decide the answer.

---

FAQ

---

Next step

Tell us which stage you are at. For selection, send the electrical requirement plus the height
ceiling, the dissipation and the AEC-Q200 requirement. For cross-reference, send the incumbent
part numbers. For production, send the annual volume and the on-site dates. Venatech Limited,
an authorised Walsin distributor in Hong Kong, will return candidates resolved against Walsin’s
parametric data with a mismatch column on every field.

Send your BOM to Venatech · Browse the Walsin inductor range ·
Read Rated current vs saturation current in chip inductors
and How to cross-reference an MLCC properly.