getting your multilayer board fabricated: assumptions can be costly, so communication is more critical than ever.

by:Rocket PCB     2019-08-19
For oem and EMS providers, it is important to understand any factors that affect the manufacture of multi-layer boards.
Multi-layer boardsonce averages less than six layers, but now it\'s usually starting with four layers, reaching 40 or more.
At present, the size, shape and form of PCBs are different.
Manufacturing multiple processes
It is more challenging than a single board for a single boardor double-
Just because the multi-layer board involves many very clear steps and processes.
There are seven or eight manufacturing phases, each of which must be properly planned and executed.
There is a great possibility of different problems at each stage, and each problem has different meanings, thus minimizing production.
The first obstacle is the placement of manufacturing notes.
For various reasons, OEMs are often vague about their notes placement and labeling.
Other related issues involve hole drawings, stacking information, material labeling, and plate thickness.
In some cases, the lack of detail is due to a lack of experience or carelessness.
The consequences can be expensive, especially from time-to-
Market prospects.
For example, two-
Poor manufacturing instructions for Dayquickturn board manufacturing Overview can suspend the project until the OEM addresses these issues correctly.
It is of particularly important significance in layered and fixed high hovering.
Speed design because it determines the impedance control specification of the board.
In order to keep the signal clean and clear and suppress noise and crosstalk, traces of impedance control are required.
To suppress the noise, a trace was clipped between the two floors.
Unless the stack is defined correctly, the finished product may not be available at 5--
10% tolerance of customer expectations.
If the OEM fails to provide the details of the stack, the manufacturing plant is forced to make the assumption, but the details must be confirmed with the OEM.
On the other hand, when the stacking details are provided, the appropriate fabnote should be called up for any type of impedance, as shown in Figure 1.
Could be single-
Multiple single-ended differential pairs
End impedance of the same layer on the same layer or multiple differential pairs plate.
The board will need to integrate back factors and other compensation to provide OEM with impeachment targets originally from stackup information. [
Figure 1 slightly]
Material if there is no specified material at the time of production, there may be alternative materials in stock.
This is especially important if the circuit board is a hybrid, it has a variety of materials such as FR-
4, polyamide, Rogers or Teflon-
Basic materials (FIGURE 2). [
Figure 2:
But there is a warning.
Sometimes in high
Speed Design, different versions of a material such as FR408, may have resin structures from different suppliers.
The substrate is made of glass with different structures inside the laminate, which means that some manufacturer\'s products are more suitable for high
Faster than other designs.
For example, although it is the same fr408 material, a material manufacturer may place the resin at the point of making the circuit board pair high-speed use.
Of course, this question is 40-
Layer design than afour-layer.
For foreign materials such as nylon, Teflon or Rogers, it becomes more important to exchange materials.
This is because sometimes the manufacturing plant does not have the inventory of these materials, and the lead time for obtaining these materials may be three weeks.
After a period of time, running the motherboard repeatedly became a major issue and the OEM was unable to obtain the product in time because he did not call for the use of multiple materials in the manufacturing instructions.
One solution to the problem of foreign materials is: when the circuit board is designed and laid out, the service bureau or OEM should work closely with the manufacturer and inform the store of the specific materials required.
Although it will take a few weeks of lead time, the board knows in advance the specific type of material required for a particular board, and there are no unexpected surprises in terms of material lead time.
Netlist verification Nedist verification is the key to successful manufacturing of multi-board.
OEMs typically provide electronic data to the board in a Gerber file format.
The Gerber file is basically unintelligent data that actually represents A trajectory from point \"A\" to point \"B\", A given set of XY coordinates coordinating with another set of xy coordinates, and so on.
However, complex cad packages generate IPC-
The 356 nedist format can be integrated into any type of DFM software and motherboard.
When the board is manufactured, it is validated against the IPC356 network list.
This is the only correct way to create a network list and verify the Assembly board against IPC-356 netlist.
Sometimes, OEM customers don\'t know IPC-
356 netlist is the gold netlist used to verify board manufacturing.
In these cases, the manufacturing company creates its own network list by extracting data from the gerber Filee.
Intelligent data.
In short, when the finished PCB is validated with the data generated from the same board, anetlist will be created from the Gerber file data, which in turn is used to make the board.
This test makes little sense because it is not an industry-standard list of IPC networks and cannot detect all errors that may have entered the motherboard.
As shown in figure 3, design rule check (DRC)
Must be initiated with an OEM customer and then resolved at the root level of OEMlocation. The reason?
The OEM has the database source for these design files.
By creating DRC at the database level before submitting to the manufacturer, the OEM guarantees that the integrity of the database will not be compromised.
It\'s clean and all the issues are focused on resources, not at a later stage, sometimes with no options available.
If a plate shop finds an error throughout the process, some errors may not be fixed.
As a result, the whole project may have to be canceled. [
Figure 3 slightly]
Having the right equipment in the manufacturing plant is also guaranteed
Manufacturing quality of multi-board.
Is there an AOI machine?
How new are their rigs, slot machines, scoring machines, Etching tanks and testing systems?
The newer the equipment, the higher the possibility of multi-board quality.
The device must be configured in accordance with the specifications provided by the equipment manufacturer.
Manufacturing companies are based on familiarity with their equipment, and almost every job is changing.
Therefore, the equipment needs to be new and automated, so these processes are minimal, for example, when a technician inserts a compensation factor for plating, etching, and adjusting the weight of copper.
AOI machines are especially important for checking the internal layers of the board and ensuring that there is enough clearance for the internal traces.
Once all the internal layers are laminated, there is no way to check the final plate except with the tester.
It is best to deploy AOI machines after the internal layer is assembled, and then deploy.
By doing so, errors can be captured, sufficient gaps are guaranteed, and fab technicians can ensure that DRC is performed on internal personnel before lamination.
Short or open inside may be ignored without AOI.
Normally the internal opening and the shorts cannot be fixed and the item must start from scratch.
For this and other reasons, fab house must embed quality assurance steps in its process flow chart to ensure that the board is ready for the final stage.
In addition, the chemical should be analyzed regularly to ensure the correct chemical, which can prevent excessive circuit board
Corrosion in the process of corrosion.
If it is over-corroded, the trace becomes thinner, the signal is not carried properly, and it may turn on the trace if the high current is running.
If it\'s etched, trace-to-via andtrace-to-
Copper is short.
Therefore, the Etchback factor and plating compensation must be done correctly.
In this regard, the oem checks the etching and electroplating process of the manufacturing plant to determine if the supplier has
An indoor chemical laboratory that conducts regular analysis.
Outsourcing processes it is also important to know which processes the manufacturer is performing in
The ability of the house, which are outsourced, and those outsourced engineers.
Figure 4 shows the \"typical\" multi-layer manufacturing process.
PCB surface finish types such as HASL, gold immersion or silver immersion are some common outsourcing processes.
Sometimes, testing and plating are outsourced.
However, it is best to keep as much work as possible-
The house is tightly controlled and does not need to rely on a second, third or fourth source.
But even if these processes are-
Additional care should be taken to verify OEM information and calculations.
The smart house does not accept OEM calculations--i. e.
, Related to the thickness of the impedance control stack--
The last sentence.
Instead, they do their own impedance control calculations and verify them based on the information provided by the OEM.
In addition, when the OEM places the order and returns the same order after six months, this is considered a duplicate order, for the manufacturer, it is very important to maintain strict document control over this particular job to maintain the revision level.
Many times, OEMs demand two, three or more different views of the same product, sometimes with little change.
If the document control does not maintain the appropriate revision level, the results can be very expensive and time consuming ---
It may take thousands of dollars and weeks to correct these errors.
Finally, the OEM should give extra time to the highly complex multi-layer board design instead of thinking it\'s two-or three-day quickturn.
This is especially true for a tight design of 3-
5% tolerance for Impedance Control, multiple differential pairs and foreign materials. Time-to-
The market is important, but more importantly, it will take 5 to 7 days to make such a board correctly.
Zulki khan is the president and founder of NexlogicTechnologies (SanJose, CA); zk@nexlogic. com.
Phil lerma is the manufacturing service manager of Nexlogic; phil@nexlogic. com.
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