PCB Assembly FAQs (Part 2)
1. Does the red dot means pin 1 in the placement previewer?
Generally, we do not call the red dot pin 1, but a marking only, which is used to indicate the orientation of the components. As shown below, basically, there will be a dot on the component itself, and there will also be a dot on the PCB (silkscreen), when they match, that means the component is placed correctly.
Figure 1. The dots on PCB and components
Figure 2. The red dots
2. What if the orientation for the component showing wrong in the placement preview?
The 0 degree that you defined for your design may be different with the one that we defined, but we both use the same rotation. So, sometimes you will find that there are some components in the wrong orientation. In this case, you can modify the rotation in your pick&place file and get it corrected. If you don’t know how to change the file, please just place your order, our engineers will review and fix the rotation and polarity of the components based on the silkscreen markings before assembly.
3. About the "0" degree for the package
There is only one simple rule: Zero orientation for PCB library should match the component orientation in the packaging(tape/reel).
In most datasheets, how components are placed in the package is described. Please also note that some manufacturers put this information in a separate file, just google manufacturer name with "tape and reel" you can find the PDF. For example, if you search "on semiconductor tape and reel", you can find Tape & Reel Packaging Standards. Some examples are listed here.
Figure 3. Zero degree of SOT23-3 (ON-Semi)
Figure 4. Zero degree of SOT23-5 (ON-Semi)
Figure 5. Zero degree of SOIC-8
Even for the same package from the same manufacturer, they may have different orientations in the tape for different components, please pay attention to the part number and refer to the tape & reel packaging standards provided by the manufacturer.
4. The reasons of different price for the component
For most of the SMD components, it requires a minimum quantity to process PCB assembly, or extra parts to cover possible attrition during assembly process, so there is a minimum order quantity required. When the quantity of the components you required does not reach the minimum quantity, it will charge the fixed fee as the minimum Qty required. Please note that unused parts will not be sent because they are discarded directly in the production process.
5. When the components will be restocked?
Usually our purchasing department will have their own purchasing plan, they will evaluate the purchase time based on the remaining inventory. However, since the delivery date is unpredictable, we don’t know the specific arrival time either, but you can check it on the website regularly. If you are in a hurry to place an order, it is recommended that you first check whether the component is in stock or not.
6. Why there is in stock on LCSC website but not in JLCPCB library?
The reason is that our components sources are from LCSC, and LCSC has two warehouses located in Jiangsu and Shenzhen. So sometimes the components are shown available on LCSC website, but it shows 0 when you are placing an order. This situation is caused by different warehouses sources, and we have no way to transfer them.
7. What components will we assemble?
Generally, we only assemble those components which you have confirmed when ordering. If you haven’t click the “confirm” button for the components, even if they occurs in the BOM file, we will not assemble them for you. Please kindly check and make sure you have not missed any components when placing the order.
8. About the +/- symbol in the DFM
There is always a marking in the components which is very important in the DFM ANALYSE. For diodes, '+' indicates the anode and '-' indicates the cathode. For polarized capacitor, '+' indicates the anode. Also, the red dot indicates the marking on IC.
9. Why PCB order does not support Review Before Payment?
Usually, when you place a PCB assembly order, the system will occupy the components first, and other customers can no longer use the components you occupied. Due to various problems such as jet lag, once the order cannot be paid in time, the components will be occupied continuously, which will hold up the resources and other people will not be able to use them. So the assembly order needs to be paid first.
10. How do we judge the polarity for the components?
There are 2 situations:
- Basically, we will judge them according to your silk layer. If there is no silk layer or no points for us to judge how the components should be on your PCB, we cannot recognize the correct polarity. Then we will confirm with you via email. Due to the time difference and other uncontrolled issues, it will cause production delays. Therefore, we recommend you add silkscreen layer to your PCB so that we can confirm them easier and faster to avoid production delay.
- When there is a mark point in the silkscreen layer, but it is inconsistent with your CPL file. In this case, we will make the placement according to the silkscreen layer by default. Thus please make sure your file is correct to avoid misunderstanding.
For example, for the component C1, the “+” (Anode) is matched with the mark point in your silk layer by default, but in your CPL file it is reversed (as picture 2), then we change the polarity from the original part placement into a corrected part placement according (as picture 1) to the silkscreen layer in the file without asking.
11. Why the components price is different from last order?
As you know, some of our components resource is from LCSC, since we have different purchasing channels, times and quantities, sometimes the price of components will be different between JLCPCB and LCSC. Meanwhile, we have our own parts warehouse, each time we restock the components, the price will be different as well due to the three conditions mentioned above. Please refer to the price on the website at the time of the ordering. And considering the drop rate during production, we will prepare some spare components for assembly. Usually, the spare components fees will be included in the total components' fee too.