A high-Q, low-ESR MLCC is a Class I ceramic capacitor built to lose as little RF energy
as possible. Walsin Technology (Walsin) covers this with three series: HH for high-Q,
low-ESR work from 0201 to 0805, RF for microwave use, and UF for ultra-microwave designs
needing ±0.02 pF tolerance. Pick on frequency, tolerance and case size.
What is a high-Q, low-ESR MLCC and when do you actually need one?
Q is the ratio of a capacitor’s reactance to its equivalent series resistance. A high-Q
part converts less of your signal into heat. You need one wherever loss directly costs
performance: matching networks, filter arms, VCO tanks, LNA input networks and power
amplifier output stages. Below about 100 MHz, a general purpose NP0 part is usually fine.
Above that, ESR starts to dominate. Q falls as frequency rises, because dielectric loss
and electrode resistance both climb while reactance falls. In a matching network, ESR
appears in series with the signal path, so every milliohm is insertion loss. In a PA output
network, that same ESR turns RF power into self-heating, which shifts capacitance, which
detunes the network.
All three Walsin series that address this are NP0 (Class I) throughout. Every part in our
extract of all three is NP0. Class II dielectrics have far higher loss tangent and are not
usable here at any case size.
What is the difference between Walsin’s HH, RF and UF series?
HH is the high-Q, low-ESR general RF family. RF is the microwave family, which extends
down to 0201 and carries the widest voltage spread. UF is the ultra-microwave family,
narrowed to very tight absolute tolerances for tuning-critical positions. The dielectric is
NP0 in all three. What changes is case size coverage, tolerance granularity and catalogue
depth.
| Series | Walsin name | Parts in our extract | Case sizes seen | What it is for |
|---|---|---|---|---|
| RF | Microwave Caps_(RF series) | 3,615 | 0201 upward | Broad microwave coverage, several voltage ratings per value |
| HH | High Q & Low ESR Caps_(HH series) | 1,709 | 0201, 0402, 0603, 0805 | General high-Q RF, where board area allows a larger case |
| UF | Ultra Microwave Caps_(UF series) | 285 | 0201, 0402 | Tuning-critical positions needing ±0.02 pF |
The HH series splits across case sizes more evenly than most engineers expect. Our extract
holds 514 parts at 0603, 509 at 0402, 469 at 0805 and 217 at 0201 — 1,709 in total. The
0805 count is the one worth noting. High-Q RF design is usually assumed to push toward the
smallest case available, yet Walsin carries nearly as many 0805 HH parts as 0402 ones,
because larger electrodes lower ESR at moderate frequencies.
UF is the shallowest of the three at 285 parts. Treat it as a tuning series, not a bulk
series. A value missing from UF very often exists in RF at a looser absolute tolerance.
Datasheets:
High Q & Low ESR (HH) —
https://www.passivecomponent.com/wp-content/uploads/datasheet/WTC_MLCC_HQ_Low_ESR_HH.pdf
Microwave (RF) —
https://www.passivecomponent.com/wp-content/uploads/datasheet/WTC_MLCC_Microwave_RF.pdf
Ultra Microwave, narrow tolerance (UF) —
https://www.passivecomponent.com/wp-content/uploads/datasheet/WTC_MLCC_Microwave_Narrow_Tol_UF.pdf
How do I read the tolerance code on a sub-picofarad capacitor?
Below 10 pF, tolerance is stated as an absolute value in picofarads, not a percentage. In
Walsin’s coding, P is ±0.02 pF, A is ±0.05 pF and B is ±0.1 pF. On a 0.1 pF part, B means
the delivered value can sit anywhere from 0 pF to 0.2 pF. That is a 100% window, and it is
the single most common surprise in RF capacitor selection.
Here are seven real 0.1 pF and 0.2 pF parts from our catalogue extract. The reference is
RF03N0R1B250. The right-hand column states field by field what matches and what does not.
| Walsin part number | Series | Size | Capacitance | Tolerance | Rated voltage | L × W × T (mm) | Match / mismatch vs RF03N0R1B250 |
|---|---|---|---|---|---|---|---|
| RF03N0R1B250 | RF | 0201 | 0.1 pF | ±0.1 pF | 25 Vdc | 0.60 × 0.30 × 0.30 | reference part |
| RF03N0R1A250 | RF | 0201 | 0.1 pF | ±0.05 pF | 25 Vdc | 0.60 × 0.30 × 0.30 | match: series, size, capacitance, voltage, all three dimensions · mismatch: tolerance tightened to ±0.05 pF |
| RF03N0R1B100 | RF | 0201 | 0.1 pF | ±0.1 pF | 10 Vdc | 0.60 × 0.30 × 0.30 | match: series, size, capacitance, tolerance, dimensions · mismatch: 10 Vdc rating, not 25 Vdc |
| RF03N0R1B500 | RF | 0201 | 0.1 pF | ±0.1 pF | 50 Vdc | 0.60 × 0.30 × 0.30 | match: series, size, capacitance, tolerance, dimensions · mismatch: 50 Vdc rating, not 25 Vdc |
| UF03N0R1A101 | UF | 0201 | 0.1 pF | ±0.05 pF | 100 Vdc | 0.60 × 0.30 × 0.30 | match: size, capacitance, dimensions, NP0 · mismatch: UF series not RF, tolerance ±0.05 pF, 100 Vdc rating |
| UF15N0R1P500 | UF | 0402 | 0.1 pF | ±0.02 pF | 50 Vdc | 1.00 × 0.50 × 0.50 | match: capacitance, NP0 · mismatch: UF series, 0402 footprint, ±0.02 pF tolerance, 50 Vdc, every dimension |
| HH15N0R2A500 | HH | 0402 | 0.2 pF | ±0.05 pF | 50 Vdc | 1.00 × 0.50 × 0.50 | match: NP0 dielectric only · mismatch: HH series, 0.2 pF not 0.1 pF, 0402 footprint, ±0.05 pF, 50 Vdc, every dimension |
Note what the RF series does with a single value. The same 0.1 pF sits at 10 Vdc, 25 Vdc
and 50 Vdc with identical outline dimensions. Voltage rating is not what you are buying at
these values — you are buying tolerance and the loss performance of the series.
Does case size change Q and self-resonance at RF?
Yes, in two opposing directions. A larger case has larger electrodes, so lower ESR and
higher Q at moderate frequencies. A smaller case has less package inductance, so a higher
self-resonant frequency. The crossover sits where your operating frequency approaches SRF.
Above SRF the part is inductive and no longer a capacitor.
That is why catalogue depth matters. In HH, 0201 is the thinnest option at 217 parts, while
0603 is the deepest at 514. If your design runs below roughly 1 GHz and board area allows,
the larger HH cases give more choice and lower ESR. At millimetre-wave, or under a shielded
module, the 0201 RF parts hold 0.60 × 0.30 × 0.30 mm to ±0.03 mm on every axis — and on a
microstrip network that outline tolerance holds the pad-to-pad parasitic repeatable.
Can I use a general purpose NP0 capacitor in a matching network?
Sometimes, below about 100 MHz, at low power, in a non-critical position. Not otherwise. A
general purpose NP0 part shares the dielectric class but not the electrode metallurgy,
layer design or ESR target of an RF series. The dielectric code tells you about temperature
stability. It tells you nothing about loss at 2.4 GHz.
The practical test is whether loss in that position shows up in a specification you have to
meet. If it affects noise figure, output power, efficiency or filter insertion loss, use an
HH, RF or UF part.
One thing to check before you order any of these part numbers
Walsin’s MLCC parametric export omits the CT packaging suffix. Every part number in the
table above is the base part number as exported, and is not orderable as-is without the
packaging code appended. This is a quiet trap: an engineer copies a part number out of the
parametric search into a BOM, and the BOM line fails at the point of order. Venatech
Limited, an authorised Walsin distributor in Hong Kong, resolves the packaging suffix
against your reel or tape requirement before the line is quoted.
The same export has a second limit worth knowing. Walsin’s parametric download fails above
roughly 10,000 rows, so large series have to be extracted in slices. The RF series, at
3,615 parts, sits inside that limit. Several resistor families do not, which is why parts
of the catalogue are harder to see than they should be.
Frequently asked questions
What does high Q actually mean in a capacitor specification?
Q is reactance divided by equivalent series resistance at a stated frequency. A Q of 1,000 at 1 GHz means the reactance is a thousand times the ESR at that frequency. Q is not a single number for a part — it falls as frequency rises, so it must always be quoted with the measurement frequency.
Is ESR the same as ESL?
No. ESR is equivalent series resistance and causes loss and heating. ESL is equivalent series inductance and sets the self-resonant frequency. ESR determines how much energy you lose; ESL determines the frequency above which the part stops behaving as a capacitor. Both matter in RF design, for different reasons.
Which Walsin series should I start with for a 2.4 GHz matching network?
Start with the RF microwave series at 0201 or 0402. It is the deepest of the three at 3,615 parts and covers several voltage ratings per value. Move to UF only where your tuning resolution demands ±0.02 pF. Confirm against the series datasheet curve for your frequency.
Why is the UF series so much smaller than the RF series?
UF is a narrow-tolerance tuning series, not a bulk catalogue. Our extract holds 285 UF parts against 3,615 RF parts. Tight absolute tolerances require tighter selection, so fewer value and voltage combinations are offered. Use UF where the tolerance is the requirement.
Can I substitute a ±0.1 pF part for a ±0.05 pF part at 0.1 pF?
Only if your network tolerates a value between 0 pF and 0.2 pF. At 0.1 pF nominal, ±0.1 pF is a 100% window. In a matching network that generally means retuning. Check the sensitivity of your network to that node before treating the looser part as usable.
Are HH, RF and UF parts available in Hong Kong?
Venatech Limited holds Walsin catalogue data for all three series and stocks against demand. Stock is a moving snapshot, so send the value, tolerance, case size and voltage you need and we will check current availability rather than quote a figure that will be stale.
Next step
Send us the capacitor lines from your RF schematic — value, tolerance, case size, voltage
and operating frequency — and we will return the HH, RF and UF candidates with a field-by-
field match and mismatch table, plus the correct orderable part number including the
packaging suffix. We will not tell you a part is equivalent. We will show you where it
differs.
Send us your BOM → · Browse Walsin MLCC →
Related reading: NP0 vs X7R vs X5R: which MLCC dielectric ·
How to read a Walsin MLCC part number
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.