diff --git a/lib/mesh-generation.ts b/lib/mesh-generation.ts
index 1df41fe..260dc1f 100644
--- a/lib/mesh-generation.ts
+++ b/lib/mesh-generation.ts
@@ -327,44 +327,44 @@ export async function generateComponentMeshes(
       renderBoardTextures: false,
     })
 
-    // Extract or generate triangles from component boxes
-    const allTriangles: GLTFTriangle[] = []
+    // Create one ManifoldSolidBrep per component box so each box forms a valid
+    // closed manifold surface. A ClosedShell requires a single connected closed
+    // surface — merging all boxes into one ClosedShell produces invalid STEP
+    // topology that viewers silently discard.
     for (const box of scene3d.boxes) {
-      if (box.mesh && "triangles" in box.mesh) {
-        allTriangles.push(...box.mesh.triangles)
-      } else {
-        // Generate simple box mesh for this component
-        const boxTriangles = createBoxTriangles(box)
-        allTriangles.push(...boxTriangles)
-      }
-    }
+      const boxTriangles =
+        box.mesh && "triangles" in box.mesh
+          ? box.mesh.triangles
+          : createBoxTriangles(box)
+
+      if (boxTriangles.length === 0) continue
 
-    // Create STEP faces from triangles if we have any
-    if (allTriangles.length > 0) {
       // Transform triangles from GLTF XZ plane (Y=up) to STEP XY plane (Z=up)
-      const transformedTriangles = allTriangles.map((tri) => ({
-        vertices: tri.vertices.map((v) => ({
-          x: v.x,
-          y: v.z, // GLTF Z becomes STEP Y
-          z: v.y, // GLTF Y becomes STEP Z
-        })),
+      const transformedTriangles = boxTriangles.map((tri: GLTFTriangle) => ({
+        vertices: tri.vertices.map(
+          (v: { x: number; y: number; z: number }) => ({
+            x: v.x,
+            y: v.z, // GLTF Z becomes STEP Y
+            z: v.y, // GLTF Y becomes STEP Z
+          }),
+        ),
         normal: {
           x: tri.normal.x,
           y: tri.normal.z, // GLTF Z becomes STEP Y
           z: tri.normal.y, // GLTF Y becomes STEP Z
         },
       }))
+
       const componentFaces = createStepFacesFromTriangles(
         repo,
         transformedTriangles as any,
       )
 
-      // Create closed shell and solid for components
       const componentShell = repo.add(
         new ClosedShell("", componentFaces as any),
       )
       const componentSolid = repo.add(
-        new ManifoldSolidBrep("Components", componentShell),
+        new ManifoldSolidBrep("Component", componentShell),
       )
       solids.push(componentSolid)
     }
diff --git a/test/basics/basics04/basics04.test.ts b/test/basics/basics04/basics04.test.ts
index 3c5e84c..5737b76 100644
--- a/test/basics/basics04/basics04.test.ts
+++ b/test/basics/basics04/basics04.test.ts
@@ -22,9 +22,11 @@ test("basics04: convert circuit json with components to STEP", async () => {
   expect(stepText).toContain("CIRCLE")
   expect(stepText).toContain("CYLINDRICAL_SURFACE")
 
-  // Verify we have multiple solids (board + components)
+  // Verify we have one solid per element: 1 board + 2 component boxes = 3 total.
+  // Each component box must be its own ManifoldSolidBrep (issue #6: merging all
+  // boxes into a single ClosedShell creates invalid STEP topology that viewers discard).
   const solidCount = (stepText.match(/MANIFOLD_SOLID_BREP/g) || []).length
-  expect(solidCount).toBeGreaterThanOrEqual(1)
+  expect(solidCount).toBe(3)
 
   // Write STEP file to debug-output
   const outputPath = "debug-output/basics04.step"