Having worked in plastic component design for a while, you'll find it's not just about "designing products and drawing blueprints." It's more like dancing on a tightrope, balancing precision, strength, cost, and manufacturability. Below, I'll share some of my understanding based on my experience and industry case studies.

Connector shell, seemingly simple—just a plastic box—is incredibly complex. Its design has two primary goals: to provide a stable and reliable "home" for precision terminals, to be mass-produced efficiently and at low cost.

 

1. Material Selection: Eternal Battle Between Performance and Cost
This is the first step, setting tone. Choosing wrong material renders all subsequent designs meaningless.
LCP (Liquid Crystal Polymer): "Trump card" for high-frequency, thin-walled, high-temperature (e.g., SMT reflow soldering) connectors. Excellent flowability, capable of filling extremely complex thin-walled structures, superior dimensional stability, and shrinkage rate as low as 0.05%. However, its main drawback is its high cost and relatively poor toughness, making it brittle.
PPS (Polyphenylene Sulfide): High heat resistance, high rigidity, high dimensional stability, and V0 flame retardancy, making it a common choice for automotive and industrial connectors. Adding fiber further stabilizes its performance. However, it is also relatively brittle and has moderate impact strength.
PBT/PET: King of cost-effectiveness, with a balanced mechanical, electrical, and chemical resistance. PBT has better toughness, while PET has better rigidity and higher temperature resistance. However, its water absorption rate is higher than previous two, resulting in relatively poor dimensional stability and sensitivity to humid environments.
PA (Nylon): Good toughness and abrasion resistance, but its high water absorption rate causes dimensional changes, usually requiring modification (e.g., PA66 GF) or use in non-precision parts where dimensional insensitivity is not a concern.
Selection Logic: First consider operating environment (temperature, humidity, chemical media), precision requirements (spacing, coplanarity), and assembly process (whether wave soldering/reflow soldering is required), then weigh cost. One piece of advice: For connectors with a high number of pins and a small pitch (e.g., below 0.5mm pitch), LCP is almost the only option. Don't skimp on this; otherwise, mold adjustments will be incredibly difficult.
2. Wall Thickness Design: Uniform! Uniform! And more uniform!
Connector wall thickness is typically very thin, 0.4mm-0.8mm being norm. Core rule is to keep wall thickness as uniform as possible. Abrupt changes are root of all evil—shrinkage, stress, warpage, and insufficient filling all follow. If variations are unavoidable, use a gradual transition, ideally with a change rate not exceeding 25%, and increase fillet radius. Ribs are a magic bullet for improving rigidity and preventing deformation, but rib thickness is recommended to be 40%-60% of main wall thickness; otherwise, back side will shrink.
3. Draft Angle: Limit Between Precision and Demolding
To maintain precision and mating dimensions of terminal holes, draft angle of connectors is often compressed to an extremely small degree. For example, in automotive connectors, draft angle is required to be no greater than 0.25 degrees, which is almost limit of mold manufacturing. Generally, a slope of 0.5°-1° for outer surface and 1°-2° for inner surface is within a safe range. For deep cavities or textured surfaces, this slope must be increased. Such a small angle poses a significant challenge to mold polishing and ejection system design; even slight errors can damage product.

 

4. "Obstacles" and Core Pulling: Root of Mold Complexity
Connector's interior is full of "obstacles"—lateral latches, locking mechanisms, and foolproof structures. These characteristics dictate that mold must use slides (mounted elements) or lifters for forming. Design should follow one principle: use lifters instead of slides whenever possible, and simplify as much as possible. Because each additional moving part exponentially increases mold cost, failure rate, and maintenance difficulty, core pulling sequence must be strictly planned; otherwise, mold will "interact" when opening and closing.

 

5. Terminal Hole and Pin Position Accuracy: Soul of Design
This is connector's Achilles' heel. Dozens or even hundreds of tiny holes require precise positioning and roundness, while also withstanding impact of molten plastic during injection molding ("impact of material flow and product shrinkage during injection molding can cause pins to bend and deform").
Solution 1: Pre-embedded Pins (Insert Molding). Metal terminals are inserted into mold first, then injection molded. This method offers the highest precision but also results in the most complex molds and limited production efficiency.
Solution 2: Post-insertion Pins. Plastic part is injection molded first, then an automatic machine presses in terminals. This method demands extremely high precision in positioning and holding force of plastic holes. "Wall thickness" between holes is often very small (some products are only 0.4mm), requiring extremely high-quality mold steel, extremely high machining precision (slow wire EDM is standard), and uniform cooling; otherwise, uneven shrinkage will directly lead to hole misalignment.
6. Snap-fit and Stop: "Tongue and Tenon" of Connectors
This is main connection method between plastic parts.
Stop: Used for initial positioning and error prevention. Mating clearance between male and female stop is generally 0.05-0.1mm on each side. An unreasonable stop clearance design (too large or too small) is one of main causes of step differences.
Snap-in: Provides holding force. Essentially a cantilever beam, key design is calculating deflection and strain to ensure no plastic deformation or breakage during repeated insertion and removal. Snap-in root must have a large radius (R angle at least 0.3-0.5mm) to eliminate stress concentration—this is a lesson learned hard way! Guide slopes should also be made at entry and exit ends.
7. Rounded Corners and Decorative Grooves: Devil's Devil in Details
All internal corners must be rounded! This greatly improves plastic flow, reduces stress concentration, and prevents cracking. At external parting line, decorative grooves (recessed decorative grooves) are often designed for aesthetics and to conceal parting line.
8. Warpage Control: A Systemic Battle
Warpage is number one enemy of connectors, especially multi-pin, thin-walled connectors. We need a multi-pronged approach:
Materials: Select low-warpage materials (such as certain modified LCPs and PPS), and pay attention to anisotropic shrinkage of fiber-reinforced materials.
Product Design: "Escape" design ("castle escape," "L-shaped escape")—hollowing out material in non-critical areas to achieve uniform wall thickness. Reinforcing ribs should be symmetrically arranged.
Mold Design: Balance gate location and number for injection, ensure uniform cooling channels. "Stability and correlation control of baseline" is key to controlling warpage and dimensions.
Process: Optimize holding pressure curve and mold temperature.

Mold is implementer of design and also a magnifying glass for all problems. Connector molds can be considered "Swiss watches" of molds.
1. Mold Type: Hot Runner is Standard
To reduce runner waste, ensure uniform filling of multiple cavities, and achieve automation, hot runner systems are almost indispensable in modern multi-cavity connector molds. However, hot runner systems are expensive and complex to maintain.
2. Parting Line Design: Clear Thinking is Essential
Choice of parting line determines product appearance, mold structure, and demolding method. Core principle: Ensure product remains on moving mold side for easy ejection.

 

Choose it as close to product's maximum contour as possible.
Arrangement of terminal pins must be considered: perpendicular or parallel to parting line? This determines whether to use a slider core pulling method or "push-through" molding.
For structures requiring coaxiality, molding should be done on same side of mold (moving or fixed mold) to ensure accuracy.

 

3. Gating System: Art of Balance
Connector gate design is a complex subject.
Gate Type: Point gates and submarine gates are the most common, capable of automatic cut-off and minimizing gate marks.
Gate Location: This is crucial for controlling warpage and weld lines. It must be simulated using CAE (Computer-Aided Flow) analysis to ensure flow balance, ensuring weld lines appear in non-stressed, non-visual areas. Never allow gate to face small cores (pin holes), otherwise material flow will bend them.
4. Molded Parts (Core) and Insert Design: Modularization and High Precision
Due to complex structure of connectors and numerous small cores, using inserts is mainstream approach (as shown in Figure 4 of document). Advantages are obvious: easier machining (can be precision machined using wire EDM or mirror EDM), easier replacement and maintenance, and easier venting. However, challenges are also significant: cumulative precision of all assembled inserts must be extremely high, otherwise it will be disastrous. Therefore, datum positioning (such as conical positioning and edge locking) is crucial.
5. Cooling System: Fast and Uniform
Connector production has a fast cycle time, and cooling time directly determines efficiency. However, due to small and dense core, it's often impossible to arrange direct cooling channels in core area. Only beryllium copper, with its excellent thermal conductivity, can be used as an insert, or conformal cooling channels (3D printing mold technology) can be employed. Sometimes, because the core is small and an insert, cooling water cannot flow through it, and only simple cooling channels can be made on mold plate – a necessary compromise.
6. Ejection System: Gentle Yet Firm
Ejection is challenging for thin-walled small connectors. High clamping force often results in whitening or even penetration during ejection.
Ejector pins need to be numerous, small, and evenly distributed in areas of high stress (such as below ribs or around boss pillars).
Flat ejector pins have a large ejection area and balanced force, suitable for thin-walled parts, but are expensive and prone to wear.
Ejector pin mating clearance is also an important venting channel.
7. Venting System: Invisible but Crucial
Incomplete venting of gas from cavity will result in insufficient material, burning, and obvious weld lines in product. Venting grooves are typically located on parting surfaces, insert mating surfaces, and ejector pin mating surfaces. Depth is crucial, generally 0.01-0.03mm (as thin as a cicada's wing). Too deep and it will cause flash (burst), too shallow and it's ineffective. Experience shows that if burnt or insufficient filling frequently occurs in a fixed location during trial molding, the first thing to suspect is venting.
8. Mold Steel and Heat Treatment: Investing in Longevity
Connector molds often require a lifespan of over a million cycles. High-hardness, high wear resistance, and high corrosion resistance mold steels such as S136, NAK80, and H13 must be selected. For materials with added glass fiber (such as LCP+30%GF), wear resistance requirements are even higher; chrome plating or nitriding treatment of mold core may be necessary. This expense cannot be skimped on; otherwise, mold will wear out quickly, precision will be lost, and yield will collapse.

Ultimately, connector plastic part and mold design are not sequential processes, but rather a continuous iterative and mutually compromising process. When product design engineers draw diagrams, they must have a mental image of mold: Can this part be demolded? Should a slider be added? Where should ejector pins be placed? How should venting be implemented?
Before mold making, mold designers must repeatedly review product drawings and propose DFM (Design for Manufacturing) modifications: Can this sharp corner be rounded? Can this wall thickness be optimized? Is strength of this clip root sufficient?
Ultimately, a successful connector project is a perfect combination of product design, mold design, materials science, and injection molding technology. It requires engineers to have both boundless creativity and meticulous caution. Smooth collaboration with mold factory is essential to produce satisfactory mass-produced products.
Connector Manufacturing Specifications and Testing Procedures