The term bridge is usually synonymous with connection or traversing areas previously unreachable. In wireless communications, the term bridging applies to providing internet connections between two wired networks over a Wi-Fi connection. In this instance, the bridge (wireless) acts as a client by logging in to a router and providing Internet connectivity that it shares with connected devices.
However, in conjunction with soldering, the term bridging has an altogether different meaning in the field of PCBA. Solder bridging is a type of error that can occur during the soldering process. It is an issue that can impact manufacturing, necessitate reworks, and also cause erratic operation in the field. Understanding how to prevent solder bridging is an issue to address for optimal board manufacturing and operation. Therefore, let's take an in-depth look at the causes of solder bridging and put forth methods of avoidance.
What is Solder Bridging?
A constant focus on nearly all electronic devices' miniaturization brings about an increasing design requirement to fit more components in ever-shrinking package sizes. Miniaturization especially brings about various manufacturing issues, especially solder bridging.
Many issues can affect the soldering process and lead to defects during board assembly. Solder bridging is a defect that occurs when two or more pads form a connection through the excessive application of solder, creating a bridge. Other soldering issues like tombstoning are more easily identifiable, but solder bridging may not reveal itself without detailed optical inspection.
An issue such as solder bridging left undiagnosed can lead to trace damage, component damage, or even short circuits. Since this is a critical concern, a solder mask can be applied to prevent excessive solder application. A solder mask is a solder resistant coating that gets added to your PCB during the fabrication process, which protects certain areas of the PCB from solder application.
Common Causes of Solder Bridging
Various conditions can and will lead to solder bridging during the manufacturing process. Solder bridging can result from the manufacturing equipment in use or even decisions one makes during the design process. The following are some of the more common causes of solder bridging:
- Incorrect stencil specifications can result in too much solder on pads for surface mount technology (SMT).
- A bad seal between the stencil and the bare board during the printing process can lead to solder bridging.
- A small pin pitch can cause a lack of adequate clearance between component pads or the absence of a solder mask.
- The imprecise or inaccurate placement of components or a diminished component lead to pad size correlation.
- Setting the reflow oven determines the temperature at which the solder wets and sets.
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How to Prevent Solder Bridging
There are several preventative measures that a CM can take to avoid the issue of solder bridging; the list below describes areas of application.
|A solder mask relief is an area on the PCB layout that does not require a solder mask application. We commonly designate these as the thin outline surrounding through-hole pads, surface mount pads, vias, and test points.
Also, a solder mask is regulated by industry standards (IPC-SM-840D), which includes shelf life, physical requirements, materials, and others.
|Solder Mask Dam|
|A solder mask dam acts as an isolation wall between the application of solder on each of your pads. Ensure you provide a solder mask dam between each of your SMT pads. In essence, it functions as an actual (physical) dam.
As a recommendation, there should be a solder mask dam between each of the pads on your SMT components. This becomes more of a requirement the smaller and more compact your PCBAs get, i.e., Integrated Circuits (ICs).
|Solder Mask Defined Pads|
|In instances (BGAs or LGAs) where you need a solder mask dam between two SMT pads, but lack the necessary room to maintain mask relief and a barrier, try using a zero solder mask expansion setting for your pads. These provide a solder mask relief that is the same size as the copper pad it is protecting.
If this is the case, you should note this in your fabrication files, thus informing your CM to leave the solder mask defined pad as is, i.e., no standard mask clearances.
|Fiducial markers are specific design markers or indicators that you utilize in the PCB design process. These alignment markers ensure that components place accurately in terms of orientation and alignment with pads. When coupled with adequate design clearances, these markers minimize the likelihood of solder bridging occurrences.|
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Although you may not control the manufacturing process as a whole, you can dictate who your company chooses for a manufacturing partner. For example, a partner like Tempo Automation possesses the experience, manufacturing equipment, and technical expertise to utilize the preventative measures to mitigate solder bridging.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to view and download DRC files easily. If you're an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in different CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on preventing solder bridging or incorporating these measures into our manufacturing process, contact us.