I work on connector and harness programmes at KONNRA, so read the disclosure as read — but I have tried to write this as I would answer a colleague, including the part where our own paperwork disagrees with itself.
Short answer
The KONNRA KR3963 is the cross-reference for the JST SDN connector, and it is the closest match I have seen in this kind of comparison. Seven published rows line up exactly — including the two that are usually the hardest to line up, the current rating's gauge basis and the housing's flammability grade. The board-in architecture matches part for part.
The one line that does not match is the metal. JST specifies the contact as phosphor bronze with a tin-plated (reflow treatment) finish. Our specification says brass, tin plated over nickel — and our own product page claims Phosphor Bronze for the same part number. That contradiction is the first thing I would ask about, and I will come back to it.
First, the thing that decides whether this family fits at all
SDN is board-in, not wire-to-board with a header. That single fact changes the bill of materials:
- Board-in: the housing itself is soldered into the PCB and the crimped contact is pressed in from above. Two parts in the mated system, and the contact goes in once, at assembly.
- Wire-to-board with a header: a wafer is soldered down, the wire half carries a housing plus a contact, and the housing plugs onto the wafer. Three parts, and repeated mating over the product's life.
So board-in gives you a lower profile, one fewer solder joint to qualify and one fewer part number — at the cost of a wire half that is not designed to be unplugged by the end user. If your harness gets plugged and unplugged in the field, this is the wrong architecture and you want a wafer-based family instead.
Our KR3963 mirrors the original exactly here: the specification's parts list is a housing and a terminal, with the wafer column reading "None", and the product page offers two components and no wafer. There is no wafer because the original has no wafer.
The seven rows that match
- Architecture — board-in on both sides, no wafer on either.
- Current — 7A AC/DC on both, and both attach it to AWG #18. This matters more than it sounds. In the last two comparisons I did at neighbouring pitches, our figure and the original's figure were both called "7A" or "5A" but sat on different conductors, which makes the agreement meaningless. Here they sit on the same one.
- Voltage — 250V AC/DC on both.
- Withstanding voltage — 1,500V AC for one minute on both.
- Insulation resistance — 1,000MΩ minimum on both, and ours names the test conditions: 500VDC for one minute between adjacent contacts per EIA-364-21B. A 1,000MΩ figure only means something against a stated test voltage.
- Applicable wire — AWG #22 to #18 on both.
- Housing material — PA66 / PA 66, UL94 V-0, natural white on both. Material, grade and colour.
That last one is worth a sentence. In earlier comparisons the materials row was consistently the weakest, because one side would publish a bare material and expect you to look up the flammability grade in a separate document. Here both companies write the same thing.
The one line that does not match: the metal
- Base metal — JST: phosphor bronze. KONNRA: brass, per our specification.
- Finish — JST: tin-plated (reflow treatment). KONNRA: tin plated over nickel.
- Part number — JST:
SDN-21T-P1.5. KONNRA:T39630BT0101A.
And our own documents do not agree with each other. Our specification says brass. Our product page says Phosphor Bronze. The terminal component page says nothing at all. The part number carries the letter B, which our own numbering uses for brass.
The part number code is decodable now, which is useful. JST's own model-number allocation for this family prints the rule: "Surface finish: T···Tin-plated (reflow treatment)" and "Material: P···Phosphor bronze." So P is phosphor bronze and B is brass in both companies' grammars. Our terminal is a BT part, and our specification calls it brass.
Why it matters, and why I am not going to resolve it by picking the document I prefer. Phosphor bronze holds more spring per unit of cross-section and is the higher-performance choice for a current-carrying contact; brass is cheaper and easier to form. JST treats the distinction as consequential in its own paperwork — its VH high-box catalogue states that if high current must be branched in parallel, you must use contacts made of phosphor bronze. So for that duty the original's position is that phosphor bronze is not optional. Our product page advertises phosphor bronze while our specification and the part-number grammar both say brass. If you are issuing a material declaration, ask which is right before you issue it, and ask whether a phosphor bronze option exists.
The finishes are also different in kind, and that part is genuinely interesting. Reflow tin means the tin is melted after plating, which fuses the coating and smooths it — the usual answer to oxide and tin-whisker risk. Tin over nickel puts a barrier between the tin and the copper alloy underneath — the usual answer to intermetallic growth that raises contact resistance under thermal ageing. One addresses the surface, the other the interface. Both are legitimate. Neither document gives a thickness in micrometres, so if you need to compare them quantitatively, ask both suppliers.
The honest limits
The insulation window is tighter than the original's at the top, and open at the bottom. JST publishes a corridor: φ1.6mm to φ3.0mm. Our specification publishes 2.50mm maximum with no minimum. So a wire with 2.6mm to 3.0mm insulation is inside the original's range and outside ours — that is half a millimetre, not a rounding error. And at the bottom end, we impose no floor where the original requires 1.6mm, so a thin-wall wire the original rejects would pass our published field. Check the gauge and the diameter separately; they are two different constraints.
And our own two documents disagree here as well. The specification says 2.50mm. The product page and the terminal page say 2.8mm. A wire at 2.7mm passes our website and fails our crimp process. Ask which document governs your quotation. This same field has been found wrong three times before in this comparison work, so I no longer treat it as reliable anywhere on the site.
Temperature. We publish −40 to +105°C. The original publishes −25 to +85°C. Ours is the wider claim, and that is the direction to be careful about — a design already qualified at the original's range does not become qualified to ours because a substitute datasheet says so. The original's figure governs. Note also that JST's own 3.96mm products do not share one range: the standard crimp VH is −40 to +105°C, the VH high-box type and SDN are −25 to +85°C, and the VH quick-connect type is −25 to +105°C. There is no such thing as "the JST 3.96mm temperature range".
Board thickness and board layout. The original publishes 1.6mm and a full layout viewed from the soldering side, with a ±0.05mm non-cumulative hole-pitch tolerance — plus a warning that its published hole dimensions do not apply from 5 circuits upward without asking. We publish no board thickness and no layout, which for a connector that solders directly into the board is the first document a mechanical engineer wants.
Circuit count. The original goes 2 to 12, and publishes an A and B dimension for every count. Our website says 2 to 15; our specification publishes no circuit range at all. If we tool 13 to 15 positions that is coverage the original does not offer — but you have nothing from us to design a footprint against, so confirm it against a specific part number.
No derating table on either side. Both companies publish 7A and stop. Both accept 20 and 22 AWG, and neither tells you what the connector carries there.
And no durability figure on either side. Neither our specification nor JST's SDN catalogue publishes a mating-cycle or insertion-cycle count. Our product page claims "long life and durability"; that claim is unquantified on both sides.
One warning that will save somebody a mistake
We sell two 3.96mm families and they are not interchangeable:
- KR3961 replaces the JST VH family. Wafer-based wire-to-board with headers.
- KR3963 replaces the JST SDN family. Board-in, no wafer.
Six of their published rows are identical — 250V, 7A, 7A at AWG #18, −40 to +105°C, 20mΩ, 1,000MΩ. Compare the two product pages and you would reasonably conclude either part will do. Compare the two original datasheets and there is no ambiguity at all: one is a header system, the other is a housing soldered flat to the board.
Pick the series by the original part number, never by the rating. If the part being replaced is a header — something like B2P-VH — the answer is KR3961. If it is a 2P-SDN housing, the answer is KR3963.
What I would ask before signing the purchase order
- Is the terminal brass or phosphor bronze? Two of our own documents disagree, and the original specifies phosphor bronze.
- If it is brass, is that acceptable for my duty — particularly if I am branching a 7A circuit in parallel?
- Is the insulation ceiling 2.50mm or 2.8mm, and which document does the quotation reference?
- What is the applicable board thickness, and where is the layout for my circuit count?
- How many positions can you actually supply, and do you offer the housing without the polarizing boss? The original ships every count as
nP-SDN(with boss) andnP-SDN-A(without), and our cross-reference only maps the one with the boss. If your board has no clearance for it, that is a part request rather than a substitution.
Where this one lands
On architecture and on the electrical table, this is the strongest cross-reference I have put together at any pitch — board-in matching board-in, seven rows level, and the current rating matching including the conductor it is based on. What it rests on is two of our own documents disagreeing about the contact metal, and the fix is a written statement rather than a redesign.
If you are working on an SDN replacement, the full comparison with every figure and its document source is here, and the part numbers and drawings are on the KR3963 product page.
https://konnra.com/jst-sdn-3-96-connector-complete-guide/
Dongguan Konnra Electronics Co., Ltd