In the selection of industrial computing core boards (CPU Modules), the interface form—i.e., how the core board physically and electrically connects to the user's baseboard—is a seemingly simple decision with far-reaching implications. It is not only a difference in physical contact methods, but also directly determines the reliability, cost, maintainability of the final product, and even the life cycle of the entire project.

The mainstream core board interface forms on the market currently include stamp holes (half holes), gold fingers (DDR3/DIMM), and LGA (Land Grid Array). This article takes specific core board models from the Ebyte knowledge base as examples to deeply analyze the engineering trade-offs behind each interface form, helping you make the wisest decision during project selection.

Stamp Holes (Half Holes)

Representative Model: Ebyte ECK10-13xA Series (based on STM32MP135)
Stamp holes adopt a half-hole process on the edge of the PCB, which is directly fixed to the user's baseboard through reflow soldering or wave soldering to form a firm mechanical connection. This is one of the most widely used forms in industrial core boards currently.

Engineering Advantages:

• Extremely High Reliability: The soldered connection exhibits far greater stability than connectors when facing vibration, shock, and long-term thermal expansion and contraction. For industrial products deployed in vibrating machinery, in-vehicle equipment, or harsh outdoor environments, stamp holes are the cornerstone to ensure long-term stable operation.

• Optimal Cost Structure: Stamp hole core boards themselves do not require expensive connectors, transferring connection costs to the PCB manufacturing process, significantly reducing the overall BOM (Bill of Materials) cost. This is extremely attractive for industrial terminal products pursuing high cost-effectiveness and mass production.

• Low Installation Height: After soldering, the core board is tightly combined with the baseboard, and the overall height is very low, which is very suitable for closed chassis or ultra-thin devices with strict space limitations.

Engineering Disadvantages:

• Non-repairability: Once soldered, the core board can hardly be removed without damage. If the core board fails, it usually needs to be scrapped together with the baseboard, or extremely tedious hot air gun soldering operations are required, resulting in very high maintenance costs.

• Slightly Higher Development Threshold: For prototype verification in the early stage of the project, the stamp hole core board requires designing the corresponding baseboard and soldering, and the flexibility for modification and debugging is low.

Applicable Scenarios: Mass-produced equipment with long-term operation, harsh environments, cost sensitivity, and no need for frequent core board replacement.

Gold Fingers (BTB Connector)

Representative Model: Ebyte ECK20-6Y28C Series (based on NXP i.MX6ULL)
The gold finger form usually means that the core board is inserted into a board-to-board (BTB) connector through the gold fingers on the edge of the board, and then realizes electrical interconnection with the baseboard through the connector. This is a typical "modular" design concept.

Engineering Advantages:

• Extreme Maintainability: This is the core advantage of the gold finger form. The core board can be easily plugged and replaced like a memory stick. If the core board is damaged, it can be directly replaced, greatly reducing after-sales maintenance costs and time. This feature is crucial for scenarios requiring fast on-site maintenance.

• Flexible Upgrade and Iteration: During the product life cycle, if a higher-performance processor or a core board with larger memory needs to be replaced, it only needs to be plugged and replaced, and the baseboard design does not need to be changed, greatly improving the evolution capability of the product.

• High Usability: During the project development phase, developers can easily replace the core board for testing and debugging, accelerating the prototype verification process.

Engineering Disadvantages:

• Increased Cost and Volume: The connector itself (including the gold fingers on the core board and the socket on the baseboard) is a significant BOM expense. In addition, the PCB area and installation height of the core board occupied by the connector are larger than those of the soldering solution, which is not suitable for extremely compact designs.

• Potential Contact Reliability Risk: In long-term high-temperature, high-humidity, and strong vibration environments, the metal contacts of the connector have potential risks of oxidation, wear, or poor contact. Although high-quality connectors alleviate this problem to a certain extent, physical contacts always have a failure boundary.

Applicable Scenarios: Small and medium-batch or high-value products that require rapid iteration, modular design, and convenient later upgrade and on-site maintenance, such as smart gateways, edge computing servers, development boards, etc.

LGA (Land Grid Array)

Representative Model: Ebyte ECK41-E Series (based on Rockchip RK3506)
The bottom of the LGA-shaped core board is a plane covered with solder pads, which is soldered to the user's baseboard through reflow soldering. It simultaneously absorbs the advantages of stamp holes and BGA (Ball Grid Array).

Engineering Advantages:

• Ultra-high Pin Density: LGA can achieve far more pins than stamp holes on the same or even smaller core board size, which is almost necessary for modern high-performance processors that need to lead out a large number of high-speed signals (such as DDR, PCIe, MIPI). For example, the ECK41-E provides rich functions through the LGA interface in an ultra-small size of 29x25mm.

• Excellent Reliability: After soldering, the mechanical strength of LGA is close to that of BGA, and its shock resistance and thermal shock resistance are better than those of gold fingers, which is very suitable for small-sized, high-computing industrial applications.

• Conducive to Miniaturization: Since the solder pads are on the bottom, the front side of the core board can fully place components, which is conducive to achieving extreme volume optimization.

Engineering Disadvantages:

• High Soldering Process Requirements: LGA soldering has high requirements for the reflow oven temperature curve, stencil thickness, and solder paste selection, and the solder joints are completely invisible after soldering, requiring X-Ray detection capability, which raises higher thresholds for production equipment and technology.

• Non-repairability: Similar to stamp holes, it is extremely difficult to remove and solder the LGA core board after it is soldered to the baseboard, making maintenance difficult.

Applicable Scenarios: High-end, miniaturized industrial applications with extreme requirements for volume, pin density, and reliability, such as portable devices, microcontrollers, and highly integrated gateways.

 A Table to Clarify the Selection

Frequently Asked Questions (FAQ)

Q1: Can I switch the interface type of the same core board model to meet different project needs?

A: Most core board manufacturers offer optional interface configurations for the same processor platform. For example, Ebyte provides both stamp hole and gold finger versions for some i.MX series core boards. However, note that different interface types correspond to different PCB footprints, and the baseboard design needs to be adjusted accordingly when switching.

Q2: Is the gold finger interface absolutely less reliable than the soldered interface?

A: Not necessarily. For indoor or mild industrial scenarios, high-quality gold finger connectors with anti-oxidation coating and locking structure can achieve 5-10 years of stable operation. Only in scenarios with long-term strong vibration, high salt spray, or extreme temperature changes, the soldered interface (stamp hole/LGA) has obvious reliability advantages.

Q3: What is the typical cost difference between the three interface types?

A: Taking the same processor core board as a reference:

• Stamp hole solution has the lowest cost, and the BOM cost of the connection part is about 1-3 USD (only PCB manufacturing cost is added)

• Gold finger solution adds 5-15 USD for connectors, accounting for 10%-30% of the total core board cost

• LGA solution has a slightly higher SMT process cost, adding about 2-5 USD compared to stamp holes, mainly for X-Ray testing expenses

Q4: I need to do prototype verification first and then mass produce. Which interface is more suitable?

A: It is recommended to choose the gold finger version for the development and verification stage to facilitate quick replacement of core boards with different configurations for testing. After the solution is finalized, if mass production requires cost reduction and higher reliability, you can switch to the stamp hole version of the same series of core boards, and only need to adjust the baseboard interface design once.

Q5: What is the maximum number of pins that the three interface types can support?

A:

• Stamp hole: limited by the PCB edge length, the maximum number of pins is usually 100-200, suitable for low-to-medium pin count processors

• Gold finger: standard edge connectors can support 200-400 pins, meeting the needs of most mid-to-high-end processors

• LGA: the highest pin density, can support more than 500 pins, suitable for high-performance processors with a large number of high-speed interfaces such as DDR, PCIe, and MIPI

Q6: Are there special requirements for the operating environment of the LGA interface?

A: LGA welding requires a precise reflow soldering process, and it is necessary to control the furnace temperature curve error within ±5°C. For small-batch production, it is recommended to use a professional SMT factory with X-Ray testing equipment to avoid hidden dangers such as virtual soldering. In terms of application scenarios, LGA has the same environmental adaptability as stamp holes, and can adapt to harsh industrial environments of -40°C to 85°C.

Q7: How to choose between stamp hole and LGA when both have high reliability requirements?

A: Priority is given to pin count and size requirements:

• If the processor has fewer than 200 pins and there is no extreme size requirement, choose the stamp hole solution, which has lower welding process requirements and lower production costs

• If the processor has more than 200 pins, or the product requires an ultra-compact design, choose the LGA solution, which can achieve higher integration in a smaller size

Q8: Will the gold finger interface affect the signal quality of high-speed interfaces?

A: High-quality gold finger connectors have been impedance-matched, and the impact on high-speed signals (such as Gigabit Ethernet, USB 3.0) is negligible within the design specification range. For interfaces above 10Gbps, it is recommended to select connectors with high-frequency performance certification and carry out signal integrity simulation verification during the baseboard design stage.

Choosing the interface form of the core board is essentially a strategic trade-off among the triangle of "reliability, cost, and maintainability". There is no absolute "best", only the most "suitable".

• When your product pursues long-term stability, optimal cost, and will work in a harsh environment until the end of its life cycle, stamp holes are the best choice.

• When your product requires frequent upgrades, fast on-site maintenance, or the project is in the development and verification stage, gold fingers/BTB bring unparalleled flexibility.

• When you need to integrate high-density pins in an ultra-small space while maintaining industrial-grade reliability, LGA provides a perfect compromise.

Understanding these engineering trade-offs will allow you to go beyond the simple comparison of "processor models" when selecting core boards, and truly make optimal decisions from the perspective of system engineering and the full product life cycle.