Learning objectives
- Form and clinch component leads to the requirements of the assembly drawing
- Seat components with correct standoff and verified polarity
- Prepare inserted boards so joints are not shadowed at wave soldering
- Protect surface mount parts on the solder side and run a first article check
Lesson
Through hole technology survives because some parts earn their place on a board: connectors that take mechanical load, transformers, large capacitors, terminals and power devices. Insertion puts those parts into plated holes before soldering. On high volume lines, axial and radial components are inserted by machine. On most modern mixed technology boards, the work is manual or uses odd form placement equipment, and the craftsmanship sits with the operator.
Preparation begins with the leads. Leads are formed to match the hole pattern and clinched after insertion, bent over in the direction and to the length the drawing and the process require. Fit comes before forming: a lead must pass through its plated hole without force, and a hole pattern that fights every lead is a problem to report, not to overpower, because forced leads spring back, lift the component off its seat and stress the hole barrel. Lead forming and cutting equipment is set and checked like any other tooling, since a former set to the wrong pitch quietly bends a whole batch of parts into scrap. A clinch that is too long can bridge to a neighbouring pad at the wave, and a clinch in the wrong direction can fight inspection and rework later. Components must seat properly, at the standoff the drawing specifies, neither floating above the board nor forced down until their seals are stressed. Forming a lead too close to the body of a component can crack its seal, damage that only appears as an early field failure. Polarity is verified part by part, because electrolytic capacitors, diodes and connectors all have a correct way round, and a reversed electrolytic is a genuine hazard under power.
Inserted boards are also prepared for the soldering that follows. Tall parts placed without thought can shadow their neighbours from the solder wave, leaving skipped joints behind them. Parts must be planned and checked with the wave or selective process in mind, and surface mount components already soldered on the underside are protected by pallets or by choosing a selective process for the through hole joints near them. Before the run proceeds, the first article is checked against the drawing, comparing seating, polarity, clinch and part identity under good light. James Onsomu teaches standard operating procedures and consistency as the foundation of lean assembly. Insertion is manual work, so the standard is the skill: same forming, same seating, same checks, every board, every shift.
Key numbers
- Lead protrusion: kept within the limits set for the product class in the governing criteria
- Clinch: direction and length as the assembly drawing and process specify
- Seating: component body at the drawing standoff, fully seated and never forced against its seals
- First article: every inserted part on the first board checked for identity, seating and polarity before the run continues
Defects to spot
- Bent or missing leads: forming faults or rough handling before insertion
- Reversed polarity: orientation checks skipped, most dangerous on electrolytic capacitors
- Floating parts: components not seated to their standoff, from poor hole fit or low insertion care
- Damaged component seals: leads formed too close to the body
- Shadowed joints waiting to happen: tall parts placed so the wave cannot reach their neighbours
Stage check, self test
Answer each question, then open the answer to check yourself. Passing standard: 80 percent, at least 4 of 5 correct.
1. Why are component leads clinched after insertion?
A. To make the board look neat
B. To hold the part in place and position the lead correctly for soldering and inspection
C. To shorten the board
D. To mark the part as inspected
Show answer
Answer: B
2. What can happen when a lead is formed too close to the component body?
A. The part becomes lighter
B. The seal of the component can crack, causing early failure in service
C. The part solders itself
D. Nothing at all
Show answer
Answer: B
3. A tall connector is inserted right beside a short through hole part. What risk has been created for wave soldering?
A. The tall part can shadow its neighbour from the wave, leaving a skipped joint
B. The board will run faster
C. The flux will last longer
D. The connector will test itself
Show answer
Answer: A
4. Which component is most hazardous when inserted with reversed polarity?
A. A ceramic capacitor
B. A resistor
C. An electrolytic capacitor
D. A mounting screw
Show answer
Answer: C
5. What is checked in the insertion first article?
A. Only the speed of the operator
B. The identity, seating, clinch and polarity of every inserted part against the drawing
C. The colour of the board
D. The packing materials
Show answer
Answer: B
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