How to Ask About and Analyze Solder Defects: Describe the Problem with 5W2H, Find the Station Where It Starts, Attach Reference Designators and Drawings — 5 Stages from Description, Station, Drawings and Mid-Chip Solder Balls to Fine-Pitch Bridging

To ask about a solder defect clearly, first write the problem as quantifiable 5W2H: which product, what defect, at which location, since when, how it was found, and in what proportion; then tell which station the defect first appears at — for example, fine-pitch bridging that is already there after printing has different causes from bridging that appears just after reflow. A technical manager at a stencil maker writes that when they do root cause analysis of a stencil, the first step is usually to obtain the reference designator of the problem part, the complete board files and the component specification drawing; larger solder balls beside chip components must first be separated from fine solder balls spattered during reflow — the former are mostly related to too much solder paste under the pad, on the inner side of the component. This article covers what to write and what to attach when asking, and how to tell apart two common kinds of shorts; the full calculation of stencil apertures, how to adjust the reflow profile and how to write an 8D report are out of scope. It is divided into 5 stages:

• Stage ① | Write the problem clearly: 5W and 5W2H, quantifiable, is and is not.

• Stage ② | Find the station where it starts: after printing or after reflow — tell the phenomena apart first.

• Stage ③ | Check reference designators, drawings and component specifications: the data root cause analysis needs first.

• Stage ④ | Mid-chip solder balls: separate them from spatter; paste volume and aperture shape; stencil thickness.

• Stage ⑤ | Fine-pitch bridging: aperture width at printing, solder mask, leads too short at reflow.

Each stage below covers: how to do it, what public sources say, and, where there is a match, what Jiahon can help with; sources, exceptions and this article’s own summaries are in the “Notes” at the end. This is the general case and still depends on the individual case.

Figure 1: The five stages of asking about and analyzing solder defects (schematic). ① Write it clearly — object: which board, which reference designator; quantity: write a proportion, not “occasionally”; comparison: what has the problem and what does not. Result: the question is asked clearly. ② Station — phenomenon: solder balls or spatter; timing: after printing or after reflow; evidence: kept at every station. Result: know which station it starts at. ③ Drawings — reference designator: find the location to look at; board files: overlay pad and stencil layers; specification drawing: compare lead and pad lengths. Result: the data is ready first. ④ Solder balls — separate: look at them apart from spatter; cause: mostly too much paste at the inner center; apertures: a home plate reduces the inner side. Result: understand the paste volume. ⑤ Bridging — printing: aperture width at half the pitch; solder mask: whether there is any between pads; reflow: leads too short may pile up solder. Result: tell which kind of bridging.

Stage ①: Write the problem clearly

How to do it:

• Where 5W comes from: the lead of a news story should answer who, what, when, where and why; reporters also use the 5Ws to guide research and interviews, and ask “how do you know?” (source 1).

• 5W2H: D2 (describe the problem) of the 8D problem-solving method requires writing who, what, where, when, why, how and how many (5W2H) in a quantifiable way (source 2).

• Is and is not: a tool commonly used in the same step is the “Is / Is Not” comparison (source 2); write down what has the problem and what does not (for example which side, which lot, which line has it and which does not), so the scope can be narrowed (this article’s own summary).

• Write numbers, not adjectives: rather than “occasional shorts”, write “so many boards out of so many in this lot, all at the same reference designator” (this article’s own summary); this is what “quantifiable” means in 5W2H (source 2).

• How you know: write clearly who found the defect, at which station, and by what method (visual, electrical test, functional test, at the customer) — the “how do you know” that the 5Ws ask for (extended from source 1; this article’s own summary).

What Jiahon Can Help With:

• When you need to photograph the location and appearance of a defect to attach to the problem description, you can use a 7-inch digital microscope (the product page says the JH-G1200 has 1 to 1,200 times continuous zoom (the JH-G1600 1 to 1,600 times), an adjustable lens angle to avoid glare, built-in photo and video functions, and instant saving as a basis for quality records and customer reports; the product page says the memory card for saving is included in the advanced accessory kit).

What public sources say: an online encyclopedia entry on the 5Ws says: the 5Ws are a checklist used in news writing to confirm that the lead contains all the key points of the story, and as early as 1913 reporters were taught that the lead should answer who, what, when, where and why; reporters also use it to guide research and interviews, asking questions such as “how do you know?”; in data analysis, the 5Ws are used at the start to confirm the business question and background. An online encyclopedia entry on 8D (the entry is marked as needing more citations) says: D2 (describe the problem) requires writing the 5W2H of the problem in a quantifiable way; the “Is / Is Not” comparison is a tool commonly used in this step, while fishbone diagrams and the five whys are commonly used in D4 to find the root cause (notes table 1).

Stage ②: Find the station where it starts

How to do it:

• First tell which phenomenon it is: when you see “solder balls”, larger solder balls beside chip components and fine solder balls spattered during reflow and landing on the solder mask are two different things with different causes: spatter may be related to the solder paste, the reflow profile or contamination on the board, while solder balls beside the component are mostly related to the amount of paste under the component; confirm which kind it is first (source 3).

• Already there after printing, or appearing after reflow: for fine-pitch bridging that is already there after printing, first look at the stencil aperture width and area ratio; bridging that is not there after printing and appears after reflow is common on gull-wing lead components, and should be checked against the lead length in the component datasheet and the pad length (source 4).

• Keep a little evidence at every station: when asking, write what was seen after printing, after placement and after reflow together; that is how you tell which station it starts at (the split from source 4; this article’s own summary).

• The cause may lie in more than one place: an EMS company’s Q&A says mid-chip solder balls may be related to the solder paste, stencil apertures, the reflow profile, placement position and skew, contamination in the paste, and ambient humidity (source 5).

What Jiahon Can Help With:

• The causes of missing components or open joints may lie in solder paste printing, stencil design, the reflow oven, PCB design or placement position; Jiahon’s engineering department can help you find the cause from these points.

What public sources say: a stencil design column on an electronics assembly industry website (December 2019; the author is the stencil technology manager at a stencil maker) says: when the pads of fine-pitch components are too wide and the stencil is not well designed, bridging may occur at printing, and then you should look at the aperture width and area ratio; bridging that is not there after printing but appears after reflow mostly occurs on gull-wing lead components, and the component datasheet is needed before root cause analysis. Another article in the same column (November 2019) says: when dealing with solder balls, the first step is to confirm that they really are mid-chip solder balls and not spatter during reflow (notes table 2).

Stage ③: Check reference designators, drawings and component specifications

How to do it:

• Get three things first: the author of the stencil column writes that their root cause analysis usually starts by obtaining the reference designator of the problem part, confirming they have the complete files used to make the board (Gerber), and also the specification drawing of the problem part (source 3).

• Overlay the component on the pads: draw the component outline and terminations as a layer and overlay it on the copper, solder mask and existing stencil layers, to see whether the pads were designed per the standard or the component maker’s recommendation (source 3).

• What was found: working this way, in many cases they found pads on the board larger than they should be, or too close to each other, with too much paste under the component or at its outer edges (source 3).

• For bridging after reflow, look at the leads: compare the lead length in the component datasheet with the pad length on the board; when the leads are much shorter than the pads, bridging may occur (source 4).

• Say if the component has been changed: pads designed for one component, later used with another of similar outline but shorter leads, often show this kind of bridging (source 4); when asking, write whether the component has been changed and which lot it changed in (this article’s own summary).

What public sources say: the stencil design column mentioned above says: contract manufacturers often have no say in board design; their root cause analysis usually starts by requesting the problem reference designator, the complete board files and the component specification drawing; overlaying the component outline on the copper, solder mask and stencil layers, in many cases they found pads larger than they should be or too close together; for bridging appearing just after reflow, compare the lead length in the component datasheet with the pads on the board, and when the leads are much shorter than the pads, bridging may occur, which often happens when pads were designed for one component and later a similar component with shorter leads is used (notes table 3).

Stage ④: Mid-chip solder balls

How to do it:

• Two kinds of solder balls: spatter happens during reflow when the flux and solder powder in the paste react with the environment and release gas violently, throwing very fine solder particles onto the solder mask, and may be related to the paste, the reflow profile or contamination on the board before reflow; mid-chip solder balls are larger and appear around the component (source 3).

• Mostly too much paste on the inner side: mid-chip solder balls usually come from too much paste, particularly at the inner center under the component (source 3).

• Aperture shape: for no-clean paste on passive components, most stencil makers start with “home plate”, “inverted home plate” or U-shaped home plate apertures, removing some of the paste at the inner center of the aperture; if solder balls still occur, the author writes they may suggest a different design and reduce the paste volume further (source 3).

• Look at stencil thickness too: a 5 mil stencil prints about 25% more paste than a 4 mil one; the same aperture design may give solder balls on 5 mil but not on 4 mil (source 3).

• Solder balls can cause shorts: an EMS company’s Q&A says such solder balls may cause shorts and lower reliability; possibly related factors include the solder paste, stencil apertures, the reflow profile, placement position and skew, contamination in the paste, and ambient humidity (source 5).

Figure 2: Mid-chip solder balls and spatter: the solder balls are larger and around the component, and the stencil aperture reduces the inner center (schematic, based on source 3; shapes and proportions not to scale). Looking down on a chip component: component body (dashed outline), pads, stencil apertures with the inner center reduced; mid-chip solder balls: larger, around the component; spatter: very fine, landing on the solder mask.

What public sources say: the stencil column article on solder balls mentioned above says: solder balls are also called mid-chip solder balls, and you must first confirm they are not spatter; spatter consists of fine solder particles caused by flux and solder powder reacting with the environment and releasing gas violently during reflow, and may be related to the paste, the reflow profile and contamination on the board; mid-chip solder balls are larger, around the component, and mostly come from too much paste at the inner center under the component; most stencil makers start with home plate, inverted home plate or U-shaped home plate apertures on passive components, and in their laboratory results the inverted home plate succeeded; a 5 mil stencil prints about 25% more paste than 4 mil. A Q&A page by an EMS company (published September 2023, modified October 2025) says: such solder balls may cause shorts and reduced reliability, with factors including the paste, apertures, reflow profile, placement, contamination and humidity (notes table 4).

Stage ⑤: Fine-pitch bridging

How to do it:

• Bridging already at printing: a common cause is pads wider than they should be combined with a poorly designed stencil; first look at the aperture width and area ratio (source 4).

• Aperture width: the author’s suggestion is an aperture width of half the lead pitch, with the aperture length the same as the pad; when the pad width is less than half the pitch, the aperture is as wide as the pad (source 4).

• Whether there is solder mask between pads: if printing still bridges with the half-pitch design, the first question is whether there is solder mask separating the pads; if not, shorts are possible, and the aperture width should be narrowed a little more (source 4).

• Area ratio: without a ceramic nano-coating, the area ratio should generally be greater than 0.60 to print 80% to 100% of the aperture’s theoretical volume (source 4).

• Bridging just after reflow: the shoulder of a gull-wing lead may heat before the pad in the oven, so the paste may melt first and climb up the lead, stop at the shoulder, and then possibly pile up around the lead; when two adjacent leads both do this, bridging may occur (source 4).

• The reductions the author gives: if the lead is 25% shorter than the pad, reduce paste volume by 10%; 50% shorter, by 25%; 70% shorter, by 40%; the new aperture should be aligned with the lead position (source 4). These are one author’s rules of thumb, not a standard.

Figure 3: Two kinds of fine-pitch bridging: for bridging already after printing, look at aperture width and solder mask; for bridging just after reflow, look at lead length and pad length (schematic, based on source 4; shapes and proportions not to scale). After printing: aperture width at half the pitch, aperture length the same as the pad, whether there is solder mask between pads. After reflow: the shoulder may heat first, molten solder may climb to the shoulder and pile up around the lead; the pad is longer than the lead; when two adjacent leads both do this, bridging may occur.

What public sources say: the stencil column article on bridging mentioned above says: fine-pitch components often have pads that are too wide, and with a poorly designed stencil, bridging may occur at printing; the author suggests an aperture width of half the pitch and a length the same as the pad; if it still bridges with this design, first ask whether there is solder mask separating the pads; the area ratio should generally be greater than 0.60; bridging appearing just after reflow is mostly on gull-wing components, where the lead shoulder may heat faster and molten solder may climb to the shoulder and pile up around the lead, so two adjacent leads both doing this may bridge; the author gives reduction suggestions according to how much shorter the lead is than the pad, and aligns the new aperture with the lead (notes table 5).

Further reading

To go through the related process steps together, you can read these next:

• “How to Troubleshoot Solder Paste Printing Defects? Work Back from What Was Printed to Which Consumable to Change“: how to troubleshoot defects already visible after printing

Notes: sources and exceptions

The following is for readers who need to check; skipping it does not affect the approach above. Where your product specifications, the customer’s quality requirements, or the data of your component and solder paste makers differ from this article, follow them.

Where each stage comes from

Table 1 | 5W2H to write when asking

Sources: 5W2H and the is/is not comparison come from source 2, and “how do you know” from source 1; what to write in each row is this article’s own summary; there is no “why” in the table: why (the cause) is what has to be analyzed, so you do not need to write it first when asking.

Table 2 | First tell which kind it is

Sources: see each row.

Table 3 | Data needed first for root cause analysis

Sources: see each row.

Table 4 | Mid-chip solder balls

Sources: see each row.

Table 5 | Fine-pitch bridging (suggestions by one stencil column author)

Source: 4 (one author’s rules of thumb, not a standard; follow the recommendations of your stencil maker and component maker).

Exceptions and limits

• What was seen: this article read 5 public sources: two online encyclopedia entries (sources 1, 2), two articles in the same stencil design column (sources 3, 4), and a Q&A page by an EMS company (source 5); the clauses of solder joint acceptance standards or stencil design standards themselves were not read.

• Sources with a position: the author of sources 3 and 4 works at a stencil maker, and the aperture suggestions come from their laboratory and experience; source 5 is an EMS company’s Q&A, and some of its wording is general; the solder balls in source 5 are small balls near the center of the joint, not entirely the same kind as the larger balls around the component in source 3.

• Conditions of the figures: 25%, 0.60 and the reductions in table 5 are one author’s rules of thumb; 5 mil and 4 mil are examples of stencil thickness; none of these are values your product should use.

• Scope: the full calculation of stencil apertures, how to adjust the reflow profile, how to choose solder paste and how to write an 8D report are out of scope for this article.

• This article’s own summary: in Stage ①, “write numbers, not adjectives” and the is/is not examples, and applying “how do you know” to how the defect was found; in Stage ②, “keep a little evidence at every station”; in Stage ③, “say if the component has been changed”; the scenario for the microscope point under “What Jiahon Can Help With”; what to write in each row of table 1; and Figures 1 to 3 (Figure 2 based on source 3, Figure 3 on source 4) are this article’s own summary; the other sentences can be matched to statements in the sources or on Jiahon’s pages.

• Equipment and products: in “What Jiahon Can Help With”, the functions and specifications in parentheses follow the product page text, and the engineering department sentence describes the scope of help from Jiahon’s engineering department; the specification is as on the product page; the scenario for the microscope point, “when you need to photograph the location and appearance of a defect to attach to the problem description”, is this article’s own summary; the link text uses the function name and does not give the product page’s model number, series code or brand.

This article is a summary of the general case, not a restatement of standard clauses, and not an endorsement of any stencil maker, solder paste maker or contract manufacturer, nor an assurance for your products and processes. Please follow your product specifications, the customer’s quality requirements, the data of your component and material makers, and your own validation; this is the general case and still depends on the individual case.