On day 28 we walked the path from spec to board on ElectroTAS’s own line. Before that we mapped the SMD line (day 22), productivity (day 23), MOQ (day 24), yield (day 25), lead time (day 26) and choosing a Zheng Bang machine (day 27). Today we zoom in on a decision that runs through that whole journey: who writes the firmware, who designs the PCB, and who assembles and tests the board? One supplier, or three passing files back and forth?
This post is a decision map: where split projects break, what you gain with a single accountable party, what should stay yours even if you delegate everything, when splitting the work is perfectly fine, and how to lower the risk of depending on one supplier. Anchors: custom electronics · pick-and-place · Downloads · shop · blog.
Where a split project breaks: the handoffs
When firmware, PCB design and assembly (SMD + THT + testing) sit with different companies, every handoff is a place where information gets lost. No bad faith is needed: it is enough that nobody owns the complete system. These are the four most common symptoms:
| Problem | How it shows up | Why it happens with separate suppliers | What changes with one accountable party |
| Handoff friction | Questions bouncing around by email, files arriving incomplete, days waiting for an answer | Each party works from its own version of the spec and its own calendar | Hardware, firmware and the line talk internally, from the same document |
| Blame-shifting | The board will not boot: the designer says “it’s the firmware”, the programmer says “it’s the assembly”, and the assembler says “it’s the design” | Nobody answers for the integrated result | A single point of contact answers for the working device |
| Revision drift | The firmware expects board revision B, but the line is building revision C with a different pinout | There is no single record of which firmware goes with which board revision | Firmware and hardware compatibility is tracked in one version record |
| Test gaps | Everyone tests their own part, but nobody tests the complete device the way the customer will use it | End-of-line functional testing is nobody’s job in particular | Acceptance criteria are designed together with the board and executed on the same line |
None of these problems is fixed with more meetings. They are solved when the boundary between firmware, PCB and assembly sits inside one team, or when, if you split the work, someone explicitly owns those boundaries. We broke down the time cost of these handoffs on day 26, and the rework cost on day 25.
One supplier vs fragmented suppliers
The table does not say one model always wins: it shows what changes for each criterion. Use it as a checklist for your own case.
| Criterion | One end-to-end supplier | Fragmented suppliers |
| Accountable for the working device | One party, for the integrated result | Spread out; integration lands on you |
| Communication | Internal, around a shared spec | Between companies, with file handoffs and separate response times |
| Firmware and board versions | One record of which firmware goes with which revision | You maintain that matrix yourself or require it by contract |
| DFM and testability | Built into the design for the line where it is assembled | Depend on the designer knowing the assembler’s line |
| End-of-line functional test | Designed together with the firmware and hardware | Often falls into no man’s land unless agreed in writing |
| Picking the best in each field | Limited to that supplier’s capabilities | Maximum freedom: you can choose specialist by specialist |
| Dependency | More concentrated; mitigate it with documentation and files in your hands | More spread out, but with more failure points at the boundaries |
| Management effort on your side | Low: one point of contact | High: coordinating schedules, versions and responsibilities |
For short series of 50, 100 or 200 boards, the typical ground for ElectroTAS’s service (the reasoning behind MOQ is on day 24), the effort of coordinating three suppliers usually outweighs the freedom to pick specialists. With higher volume and an in-house engineering team, the balance can tip the other way.
Working map: where firmware meets hardware
Most production problems show up at the boundary between firmware and board. This map lists the interfaces worth defining at design time so the line does not have to improvise them. It is a recommended working guide, not a list of contractual deliverables:
Firmware and hardware interfaces for surprise-free production
- 1. Test points
- Reachable from the side that will be tested, marked on the silkscreen and designed for a fixture, not just for a meter probe.
- 2. Programming header
- A programming connector or pads defined in the schematic, with clear orientation and reachable once the board is fully assembled.
- 3. Bootloader
- Decide before the PCB is frozen whether the device will be updated in the field (over USB, Ethernet, serial or another path) and reserve memory and logic for it.
- 4. Production programming
- How firmware is loaded into every unit of the series: at which point in assembly, from which file and at which version.
- 5. Unit identity
- Serial number, MAC address or another unique identifier, and where it is recorded.
- 6. Self-test mode
- A firmware routine that exercises inputs, outputs and communications so the functional test is fast and repeatable.
- 7. End-of-line functional test
- What is measured, against which acceptance criteria, and what happens to a unit that fails.
- 8. Version record
- Which firmware version matches which board revision and BOM, in a single table.
With firmware, PCB and assembly in the same team, this map gets closed around one table. With separate suppliers, every item is an agreement between companies. At ElectroTAS, the Production stage states that every unit is inspected and tested; these interfaces are what make that testing fast and reliable.
What should stay yours
Delegating everything does not mean handing over everything. These are recommendations for any custom development client, with one supplier or several; they are not ElectroTAS contract terms, which are defined project by project during Planning:
- Intellectual property and source code: agree in writing who owns the design, the firmware and the sources, and on what terms they are delivered.
- Manufacturing files: schematic, PCB files, Gerbers, pick-and-place position file and assembly drawings, in formats you can open.
- BOM approval: you approve the bill of materials and its substitutes; a component change should not enter the series without your sign-off.
- Acceptance criteria: this is your definition of “it works”. The supplier implements it; you sign it.
- Binaries and programming procedure: the firmware file for every released version and how it is loaded, so any unit can be reproduced.
- Change log: what changed between revisions and why, even as a simple table.
A serious supplier should have no problem with any of this. If the conversation gets uncomfortable when you ask, that is valuable information before you sign.
When splitting across suppliers is fine
A single supplier is not dogma. There are scenarios where a split model works perfectly well, as long as someone looks after the boundaries:
| Scenario | Why splitting can work | What to watch |
| You have in-house firmware engineering | Your team owns the code and you only need hardware and assembly | Jointly define the programming header, bootloader and end-of-line test |
| You already have a mature, proven PCB | You only need series assembly and testing | Hand over complete files and validate a first run before the full lot |
| One highly specialized block | Part of the system needs a specialist that a generalist supplier does not cover | Name an integrator accountable for the complete device |
| High, stable volume | At high volume, optimizing each stage separately can justify the coordination | Contracts with a shared version record and shared acceptance criteria |
| You want a second assembly source | Reduce dependency on a single production line | Transferable files and tests, with no tricks only one line knows |
The common thread: if you split, someone has to own the boundaries. If that someone is you, budget the time to do it properly.
Single-supplier risks and how to mitigate them
Putting everything with one supplier carries risks too. The honest move is to name them and reduce them from the start:
| Risk | Recommended mitigation |
| Total dependency | Manufacturing files, sources and binaries kept up to date in your hands for every released version |
| Black box | Agreed minimum documentation: schematic, approved BOM, firmware notes and test procedure |
| Versions getting muddled over time | A version record for firmware, board and BOM, reviewed at every reorder |
| Less negotiating leverage | Transferable files that let you get a quote from another supplier if it is ever needed |
| Supplier changing direction | For critical products, a file and source escrow with a third party or in your own repository with guaranteed access |
| Knowledge in too few heads | Design and test documentation that survives staff changes, on both sides |
With these mitigations, a single supplier keeps its advantages (one accountable party, fewer handoffs, integrated testing) without locking you in. It is the logic of any major purchase: trust, but keep the paperwork in order.
Why ElectroTAS can cover all three
Based on what ElectroTAS publishes on its custom electronicspage, a specialized team with extensive experience covers all three disciplines under one roof, in Martínez, San Isidro:
- Firmware and software: experience with both high-level and low-level programming languages, to choose the best fit for each project.
- Hardware and PCB: research and development, a laboratory with high-precision instruments, and hardware built with state-of-the-art components.
- Assembly: a high-capacity SMD production line, plus semi-automatic lines for THT components.
- Testing: printed circuit board testing lines and, in the Production stage, every unit inspected and tested.
- Areas of experience: LED lighting, industrial control, communication protocols, data acquisition, IoT, LoRa, GSM and Ethernet.
The stage-by-stage journey is on day 28 and the line from the inside on day 22. What today adds is the other side of the coin: it is not just an orderly process, it is one accountable party for all three parts of the device.
What this post is NOT
- It does not repeat the spec-to-board journey with stages and gates from day 28, nor the line anatomy, productivity, MOQ, yield, lead time or Zheng Bang choice from days 22 to 27: it only cross-references them.
- It is not the buying guide hub with the product map (day 30).
- It does not describe ElectroTAS contract terms: what should stay yours is a set of recommendations, agreed project by project. It does not invent prices, lead times in days, specs, certifications or client names.
FAQ
1. What does it mean to have firmware, PCB and assembly with one supplier?
The same company writes the firmware, designs the hardware and the PCB, assembles the boards (SMD and THT) and tests them. You get one point of contact who answers for the working device, instead of coordinating three suppliers passing files around.
2. Is one supplier always the better choice?
No. If you have in-house firmware engineering, a mature PCB, or high and stable volume, splitting can work well. The condition is that someone owns the boundaries: versions, programming and end-of-line testing.
3. What should I keep even if I delegate everything?
As a recommendation: intellectual property and sources agreed in writing, manufacturing files, BOM approval, acceptance criteria, binaries with their programming procedure, and a change log. This is defined project by project during Planning.
4. Why do test points and the programming header matter?
Because they are the door through which firmware enters every board and through which you verify that it works. If they are not designed in from the schematic, production has to improvise, and testing becomes slow or incomplete.
5. Do I need a bootloader?
It depends on whether you will update the device in the field. If the answer is yes, decide before the PCB is frozen, so memory, interface and logic can be reserved. Adding it later usually means a board revision.
6. How do I avoid being locked into one supplier?
Keep files and sources up to date in your hands for every released version, maintain minimum design and test documentation and a version record, and, for critical products, set up a file escrow with a third party or in your own repository.
7. Can you take over a project whose firmware or PCB was made by someone else?
Ask case by case. During Planning, whatever already exists (a previous board, firmware, schematics) is reviewed, and the team decides what can be reused and what is better redone. Write to desarrollos@electrotas.com.
8. How much does it cost and how long does it take?
It depends on your spec, complexity and volume, which is why we do not publish generic numbers. It is defined during Planning with real data. Ask for a quote at desarrollos@electrotas.com or call +54 (011) 3221-4474.
One accountable party, three disciplines, no man’s land
Firmware, PCB and assembly with one supplier is not magic: it moves the handoffs out of the boundary between companies and into a single team, with one version record, test interfaces designed from the schematic, and acceptance criteria executed on the same line. What is yours stays yours: files, agreed sources, an approved BOM, and the definition of “it works”. If you want to take your device end to end, start with custom electronics or write to desarrollos@electrotas.com.
Next in the series (day 30): buying guide hub: the ElectroTAS product map plus SMD lines, no link yet. Meanwhile, the spec-to-board journey on day 28 and days 22 to 27 on the line give you the full context.
ElectroTAS · Martínez, San Isidro · info@electrotas.com · desarrollos@electrotas.com · +54 (011) 3221-4474 · WhatsApp +54 9 11 2245-2000 · shop · blog.