Component encyclopedias teach you to recognize an R from a C. The line already knows that. What stops a China SMT traveler is disagreement: the silkscreen says one orientation, the body mark says another, the BOM is silent on whether a solder jumper ships open or closed, and pin-1 is a guess under a messy legend.
This post is those assembly-drawing locks for overseas buyers and engineers. It is not a visual catalog of every package, not a multimeter repair tutorial, and not a rewrite of the broader identification guide that already covers designators and package families.
Start from three documents that must agree
Before placement, three things have to name the same reality:
- The BOM (designator, MPN, value, package).
- The centroid / pick-and-place file (designator, rotation).
- The assembly drawing and silkscreen (polarity marks, pin-1, jumper defaults).
When they disagree, operators and AOI invent a story. Write the story first. Our Manufacturing Files page is the file grammar; this post is the orientation and jumper content those files must carry.
Jumpers are configuration, not leftover copper
A jumper is a deliberate link the product uses for options, debug or routing that could not cross. On silk it is often JP (header + shunt), SJ (solder jumper pads), LK (wire link) or a 0 Ω resistor marked 0 or 000.
Lock on the drawing:
- Default state at ship: SJ open or closed; JP shunted or open; which 0 Ω lines are stuffed.
- Who may change it after SMT: field config versus a factory ECO only.
- Do not “fix” an open SJ with a whisker of solder because it “looks unfinished.”
0 Ω parts are reflowed links, not mistakes. Removing them without an ECO is a design change. Wire links on single-sided boards belong on the assembly note with gauge and path if they are still in the product.
Polarity: silk, body and CAD rotation
Electrolytics, tantalums, diodes, LEDs and many connectors carry a body mark (stripe, “+”, flat, bevel). The board should repeat a clear cathode/anode or “+” mark in copper or silk that survives after the part is placed. If silk is under the body, add a mark outside the footprint.
When silk and body disagree, the drawing wins only if you said so—and then you still have a defect to fix in the files. Do not leave “follow the body” as tribal knowledge on one shift and “follow the silk” on another.
CAD rotation in the CPL must match the same convention the library used when the polarity mark was drawn. A 180° library error ships as a polarized reverse that continuity may not catch.
Pin-1 on ICs: notch, dot and the land that matches
ICs need a pin-1 rule the assembler can see after paste: mold notch, pin-1 dot, or bevel—and a board mark (dot, “1”, or chamfered pad legend) that matches the land pattern’s pin-1. Fine-pitch parts hide silk under the body; put the mark where a camera and a human can still see it next to the package.
BGA and some QFN parts have no useful silk after placement. Pin-1 then lives in the datasheet land pattern, the polarity fiducial scheme if you use one, and X-ray/AOI recipes—not in a hope that someone remembers the tray orientation. Our SMT PCB Assembly path assumes those library rotations were frozen with the Gerbers.
What this post leaves to sibling guides
Reading SMD resistor digit codes, package DFM, and AVL substitution rules are separate posts. Visual “what is this brown rectangle” training is the broader identification article. Here the only question is: before the nozzle runs, are jumper defaults, polarity marks and pin-1 locked so the line is not asked to identify and decide at once.
AOI and human checks without overclaiming
AOI can be taught the expected polarity mark and pin-1 corner when the library and the drawing agree. It cannot invent a default for an unlabeled SJ. First-article inspection should include every polarized designator and every jumper whose ship state matters to the product option. Continuity alone will not prove an electrolytic is not reversed if the circuit still leaks into a soft fail later.
What we are not claiming
No universal silkscreen clearance table, no claim that AOI catches every polarity reverse, and no multimeter procedure for field repair. Lock jumpers, polarity and pin-1 on the assembly drawing. Then identification on the bench is confirmation, not invention.