lang="en-GB"> First Time To Order PCB Assembly Service? A Guide to PCBWay’s PCBA - Atadiat

First Time To Order PCB Assembly Service? A Guide to PCBWay’s PCBA

PCBA or Printed Circuit Board Assembly is the process of getting the PCB components populated to the bare PCB, where Surface Mount Device or SMD parts land on the PCB surface and Through Hole Device or THD parts are inserted in the conductive holes.

Depending on the design, PCB may have components on a single side or double side with either SMD only or THD only or a mix of them. Assembly can be done manually for sure. Hobbyists or engineers may choose to grab soldering iron/station, the components, solder tin, flux, and start assembling their board.
Some would make it easier for themself by using a Stencil to put solder paste through it to the PCB pads, and later to place the components on their place manually. Moreover, the process of placing the component on the Solder pasted pads can be automated using Pick and Place PnP machines and getting or DIYing an entry-level reflow oven, talking about SMD assembly, and/or a soldering pot, talking about THD assembly.

A cheap reflow oven for small scale prototype manufacturing in lab
A build by Anthony webb of the open-source project OpenPn, an SMT pick and place system

When the development is not finished and production is not reached yet, the assembly can be done manually when assembly time is available and there is a need to cut assembly services/machines fees. Yet, automated assembly is a must during the production stage.
Some firms choose to build their in-house assembly line, but it’s more common to ask for a second party to assemble the PCB for you and ideally it should be the same PCB manufacture.

Assembling 10 PCBs of Arduino UNO as A Test

In this article, we are going to explore the PCBWay manufacturer service for PCBA. This will give an overview of the steps of this service and how to order it. This article targets people who never tried PCBA as a service before and people that usually do PCBA with other firms and like to see about PCBWay service. Although this is a sponsored content to promote PCBWay service, it will be showing real technical details and trying things in action as we are going to see in 2 parts

The first part to give some background and introductions and in the second part will examine things in real using a real PCB and PCBA order. 

At the time of writing this article, PCBWay accepts assembly for PCBs only manufactured by them, so you need to order PCB and select assembly service. To keep things practical, I chose to try the process before putting a real order. So I used one of the Arduino open-source designs, namely Arduino UNO R3, and made a dummy order to get familiar with their service.  

A build by Anthony webb of the open-source project OpenPn, an SMT pick and place system

First Step: Order the Service 

Customers need to go PCB instant quote form first, then by scrolling down there is a PCB assembly service option. By selecting it, it will open another punch of fields to fill and options to select. 

Customers need to specify a few things to get a quotation of PCBA costs.

Firstly, the customer can choose to supply PCBWay with his parts to assemble under the ‘Kitted or Consigned” option, or can supply some of the parts and rest will be supplied with PCBWay, or ask PCBWay to handle sourcing all components with “Turnkey” option.
In certain case, customer may have spare parts in their inventory and don’t want to buy new parts or maybe they will use some sensitive parts that need some papers to get, so they need to send these parts to PCBWay.

It is important to note that when you use Pick and Place machines, you need to provide some extra parts (called overages) and this have different reasons. 

PnP machine feeders need a minimum amount inside the components tape. This is due to how the feeder works (the tool that holds component tape) . Let’s say you only use 2 smd capacitors with package 1206. If you use a tape containing exactly 2 capacitors, then the PnP feeder can’t hold the very short tape that contains only 2 caps. However, while PnP machines get new enhancements, they become more efficient and require less overages. 

Moreover, PnP can mispick a part during operation, and using a vision inspection system it will reject some parts so the operator needs to have already some packup. 

These rejected parts will be in a special bin, and can be loaded manually later, but if they are resistors or capacitors, it will be hard to identify them. 

Pick and Place machine’s reject bin – Image courtesy of Macrofab 

Unused and excessive parts supplied by customers or purchased by PCBWay will be packaged and returned to the customer with the assembled boards or can either ask PCBWay to keep them on their shelf for the next order.

FAQ page from PCBWay gives some numbers of how much overages are needed, summarized in the following table:

Type Package Minimum Example
Resistors, Capacitors, Diodes 0603, 0805, 1206, 2225, SOT, SOD, MELF 50 pieces and have to exceed the required quantity by 30 assemble quantity 40 pieces – will need 70 pieces – this meets the minimum of 50 pieces plus 30 pieces over assemble quantity
Resistors, Capacitors, Diodes 0201, 0402, miniMelf, miniature packages 100 pieces have to exceed the required quantity by 50 pieces assemble quantity 80 pieces – will need 130 pieces- this meets the minimum of 100 pieces plus 50 pieces over assemble quantity
Expensive parts IC, BGA, QFP, Connectors, etc 1-5 pieces based on the total quantity of assemblies

This is important to know as this will be an additional cost when you order assembly with the “Trunky” option, and important to know if you want to supply PCBWay in “Kitted” or “Combo” option. The image below is an example of a part of BOM sent to PCBWay with overages added.

Now let see the second part of the order form, and it’s about specifying if you have components on one side or both sides and if you will do penalization or not.

for a mixed PCB with SMD and THD components like Arduino, the soldering should be on top for SMDs and on bottom for THDs, but as the components are on one side, the assembly side option in the order calculator will still be ‘top side’ only. However, the review process will double check that according to Gloria from the PCBWay team.

Knowing that, if you choose to have 2 sides assembly, when your PCB has components in the top and bottom layer, this will increase the service fees, as the process of 1- solder paste printing 2- Pick and Place components 3- reflow soldering will be repeated as the diagram below shows

The last part of the form is to declare the number of parts used in your design. Customers can leave it empty and the review process will take handle of it.

Last part of the form is to declare the number of parts used in your design. Customers can leave it empty and the review process will take handle of it.

After that, you need to upload the design Gerber files for the PCB manufacturer, and we are not going to talk about it as it is not this article scoop. You have to upload a proper BOM for your design to have a final quotation for the assembly service fee and costs of purchasing the components including the overages as we explained before. 

PCBWay provides a sample file of required BOM, and I re-used it when I sent the example Arduino UNO board Bill of material to examine the process. 

The BOM Sent to PCBWay 

Moreover, you can make your template but make sure to include the following information: 

Customers also need to provide a file used for assembly called Centroid. It is used for programming assembly machines to know the position and rotation of each component. The Centroid file includes the position and orientation of all the surface mount parts, which includes the reference designator, X and Y position, rotation and side of board (Top or Bottom). Only surface mounting parts are listed in the Centroid. 

One line example of Centroid file – Image courtesy of Numerical Innovations

Second Step: Wait for Quotation and Review  

Now, the customer needs to wait for the reviewer to review and quote the customer’s BOM and check if there is anything missed or need customer clarification. 

Keep in mind that, the price you get using the quotation calculator is only an estimation for PCB manufacturing and assembly service fees. Assembly fee would be around $30 for low quantities for average complexity circuits .

The PCB manufacturing and Assembly Service Fees for Ordering 10 pieces of Arduino UNO Design

When I sent the Arduino UNO bill of materials, I mistakenly did a copy and past of D1’s description to D2 and D3.

Then, I found an email from the reviewer asking for the problems I have in my BOM, which was a conflict in D2 description and out-of-stock of 2 parts and ask to set alternatives.

Alos the status of the order will be updated and mention that it needs customer action. 

However, this doesn’t mean that all mistakes will be discovered at this stage, as I did an intentional other conflict and it was not discovered. However, it will be discovered during the assembly stage for sure. I put one of the parts manufacturer numbers different than the description with a different package too. During assembly, the operator will catch it and communicate with me for a correction.

It is the customer responsibility to make sure that his design has no critical issues that make it impossible to assemble. For example, I made another intentional mistake in the PCB by making 2 components close in a way that will make it impossible to assemble and made one of the capacitor pads overlap with another part Pad and this affects solderability during the overflow oven stage.

However, the reviewer asked about other issues, but yet the design passed the review. So make sure you review well your design.

When I asked Gloria from PCBWay about what happened, the answer was honest and direct: Customers should take the responsibility, and moreover, if the PCB needs a modification, the customer will mostly be charged again.

In the real world, no one does mass production without a prototype!

By the end, I got the BOM with prices and the total of producing 10 copies of Arduino R3 was:

PCB x10 $5
Assemble X10 $30
BOM $230
Total $255. Around $25 per piece.

It is important to know that assembly for low quantities/ small-batch like my case will be an assembly by hand unless you have a special request to use the machine. Moreover, The overages mentioned in the last table is when the assembly is using PnP, which includes more losses than assembly manually. You can mention that the quotation for manually assembled orders do not include the overages we talked about.

A manual assembly operator matching components with BOM inside PCBWay manufacture –   Image Courtesy of “Strange Parts” Youtube channel
A manual assembly line at PCBWay manufacture – Image Courtesy of “Strange Parts” Youtube channel 

Third Step: Doing the Payment and Waiting for the Manufacturing 

At this stage, your Gerber files are reviewed and BOM is quoted and you’re ready to be charged. 

After you do the payment, PCBWay will start the manufacturing process of the PCB and later do the assembly. Meanwhile, the components should be ordered and arrive later. BOM includes notes on the lead time needed for some parts to arrive. 

So to calculate the turn time on a Turn-key order, you need to take into consideration the time needed to source all the parts. Before all parts are ready, PCBWay will fabricate the PCBs and start to make the stencil so that assembly starts immediately after they get the parts.

The Arduino UNO R3 bill of material is attached for reference.

The BOM after quotation
The quantities in the received BOM from PCBWay, have no overages. After checking with one of the PCBWay staff, I got the following reply: ” Generally, we do assembly by hand for small-batch unless the customer has a special request. We can do using machines.”.
However, this sounds reasonable as the time required to setup the machines (.i.e loading PnP’s feeders with components) for automated assembly will be too long compared to hand assembly. However, the rest process is similar.

A Closer Look of What PCBWay Do during Assembly

The assembly process may look as simple as printing PCB, then placing components and solder paste and finally enter the reflow oven. This is what I tried to explain in the diagram below.

It’s way more complicated than that and a lot of machines are involved to make your PCB assembled.

At each stage there are various testing method will be applied to the assembled boards before the final shipment:

Xray Machine inside PCBWay Manufacture – Image Courtesy of “Strange Parts” Youtube channel
AOI Machine Inside PCBWay Manufacture – Image Courtesy of “Strange Parts” Youtube channel
In-Circuit Testing inside PCBWay Manufacture – This makes sure that resistors and capacitors have a matching value to BOM – Image Courtesy of “Strange Parts” Youtube channel  

To see in action these steps behind the scene, check Scotty from “Strange Parts” Youtube channel who made a tour inside the PCBWay factory:

Inside a PCB Soldering Factory – in China – Scotty from “Strange Parts” Youtube Channel

To know more about PCBWay assembly service, please check the following Web pages. 

In the next part, I will send a real order for a PCB designed specially to test the PCBA service.

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