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steve/chip-fuse

Thin film chip fuses, Vishay MFU series, 0402, 0603, 0805 and 1206.

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part.py 49 lines · Python · STEVE runtime · checked
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1"""Thin film chip fuse, Vishay MFU series, sizes 0402 to 1206. Centred on the origin, lying on the XY plane with its length along X: the
2substrate, the protective coat on top between the terminations, and a wrap-around termination at each end (each its own solid).
3Dimensions from Vishay's data sheet; see the README."""
4from steve import Model
5
6size = "0603" # case size, inch code
7
8# size: (length L, width W, height H, bottom band (the sheet's T2), top band (T1), mass in mg), nominal values in mm.
9# Vishay Beyschlag, "MFU Series, Thin Film Chip Fuses", document 28747, revision 11-Mar-13 (https://www.vishay.com/doc?28747), page 3,
10# "DIMENSIONS - Chip fuse types, mass and relevant physical dimensions": H 0.32 +/-0.07, 0.45 +0.1/-0.05, 0.45 +0.1/-0.05, 0.55 +/-0.1;
11# L 1.0 +/-0.05, 1.55 +/-0.05, 2.0 +/-0.1, 3.2 +0.1/-0.2; W 0.5 +/-0.05, 0.85 +/-0.1, 1.25 +/-0.15, 1.6 +/-0.15; T1 and T2 0.2, 0.3,
12# 0.4, 0.5; the termination width WT is "> 75 % of W". The model uses the nominal values.
13SIZES = {
14 "0402": (1.0, 0.5, 0.32, 0.2, 0.2, 0.65),
15 "0603": (1.55, 0.85, 0.45, 0.3, 0.3, 1.9),
16 "0805": (2.0, 1.25, 0.45, 0.4, 0.4, 4.7),
17 "1206": (3.2, 1.6, 0.55, 0.5, 0.5, 9.5),
18}
19# Proportion, for looks: the terminations' and the coat's thickness, 0.1 x H (the data sheet doesn't dimension it); the terminations run
20# the full width (the sheet gives their width only as more than 75 % of W).
21SKIN = 0.1
22# The coat's top stands this far below the terminations' top bands (half the coat at most), so the renderer draws the bands' edges.
23PROUD = 0.03
24
25L, W, H, T1, T2, _mass = SIZES[size]
26t = SKIN * H
27model = Model()
28# The alumina body inside the terminations and under the overcoat.
29model.box("body", L - 2 * t, W, H - 2 * t, at=(0, 0, H / 2), op="new", body="body_body", name="Body")
30# The coat on top between the terminations' top bands, a little below them.
31coat = t - min(PROUD, t / 2)
32model.box("overcoat", L - 2 * T2, W, coat, at=(0, 0, H - t + coat / 2), op="new", body="overcoat_body", name="Overcoat")
33# Each termination: its section in the XZ plane (bottom band T1 long, the end face, the top band T2 long), extruded across the width.
34for tag, side in (("left", -1), ("right", 1)):
35 x_end = side * L / 2
36 section = [(x_end, 0.0), (x_end - side * T1, 0.0), (x_end - side * T1, t), (x_end - side * t, t), (x_end - side * t, H - t),
37 (x_end - side * T2, H - t), (x_end - side * T2, H), (x_end, H)]
38 # The XZ plane's normal is -Y: offset -W/2 puts it on the +Y face, and the extrusion runs across the width to -Y.
39 model.plane(f"{tag}_plane", on="XZ", offset=-W / 2, name="Terminations")
40 with model.sketch(f"{tag}_sketch", on=f"{tag}_plane", name="Terminations") as sk:
41 sk.polyline(f"{tag}_section", section, closed=True)
42 model.extrude(f"{tag}_term", f"{tag}_sketch", distance=W, op="new", body=f"{tag}_body", name="Terminations")
43# Materials, for looks and a rough mass (the sheet names no materials): the substrate shown as alumina, the coat as ptfe and the
44# terminations as tin, as the library's chip resistor; the mass is checked against the sheet's in the README.
45model.material("alumina", bodies=["body_body"], color="#f2efe6")
46model.material("ptfe", bodies=["overcoat_body"], color="#3a5a40")
47model.material("tin", bodies=["left_body", "right_body"], color="#c9ccd1")
48result = model.result()
49

Surface-mount thin film chip fuses for board layouts and enclosures, as Vishay draws its MFU series: the substrate, the protective coat on top between the terminations, and a wrap-around termination at each end, each its own solid. Sizes 0402, 0603, 0805 and 1206. Dimensions and mass from Vishay's data sheet. See the README.

Chip fuse

Vishay's MFU series of thin film chip fuses, in sizes 0402, 0603, 0805 and 1206. The fuse is centred on the origin, lying on the XY plane with its length along X. It is the substrate, the protective coat on top between the terminations, and a wrap-around termination at each end. Each is its own solid.

Source

Vishay Beyschlag, "MFU Series, Thin Film Chip Fuses", document 28747, revision 11-Mar-13, https://www.vishay.com/doc?28747, page 3, "DIMENSIONS - Chip fuse types, mass and relevant physical dimensions":

Size H L W WT T1 (top) T2 (bottom) Mass
0402 0.32 ± 0.07 1.0 ± 0.05 0.5 ± 0.05 > 75 % of W 0.2 +0.1/-0.15 0.2 ± 0.1 0.65 mg
0603 0.45 +0.1/-0.05 1.55 ± 0.05 0.85 ± 0.1 > 75 % of W 0.3 +0.15/-0.2 0.3 +0.15/-0.2 1.9 mg
0805 0.45 +0.1/-0.05 2.0 ± 0.1 1.25 ± 0.15 > 75 % of W 0.4 +0.1/-0.2 0.4 +0.1/-0.2 4.7 mg
1206 0.55 ± 0.1 3.2 +0.1/-0.2 1.6 ± 0.15 > 75 % of W 0.5 ± 0.25 0.5 ± 0.25 9.5 mg

The model uses the nominal values.

Proportions, stated plainly. The sheet doesn't dimension these:

  • The terminations and the coat are 0.1 times H thick. The coat stands 0.03 (0402: 0.016) below the terminations' top bands so their edges show.
  • The terminations run the full width. The sheet gives their width only as more than 75 % of W.

Materials and mass. The sheet names no materials. The substrate is shown as alumina, the coat as ptfe and the terminations as tin, as for the library's chip resistor. With those densities (3.95, 2.2 and 7.3), the model's mass against the sheet's is 0.64 against 0.65 mg (0402), 2.34 against 1.9 (0603), 4.4 against 4.7 (0805) and 10.7 against 9.5 (1206).

Catalogue models

The old catalogue's Fuse_0402_1005Metric, Fuse_0603_1608Metric, Fuse_0805_2012Metric and Fuse_1206_3216Metric have no reference models. Each names an EIA chip size, and each maps to the MFU of that size. Fuse_1210_3225Metric is left out, because the MFU series has no 1210. The family's Bel Fuse PTC fuses are the radial-ptc-fuse part's, and its fuse holders are left with their reasons in COVERAGE.md.

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