Via-in-Pad Design Considerations for Bottom Terminated Components on Printed Circuit Board Assemblies
Bibliographic record
Abstract
ABSTRACT Over the last two years, there has been a substantial increase in the usage of bottom terminated components (BTCs) within high complexity, high-reliability Server and Storage class hardware products. Component suppliers are offering a greater variety of small form factor BTCs as QFNs integrating thermal pads and thermal vias. Designers are readily adopting these packages. With their small component body footprint and minimal PCB area requirements, physical designers are keen to incorporate small footprint QFN solutions within circuit designs to meet a wide variety of voltage/power regulation, logic controller, and clocking needs. To date, the majority of published work relating to QFNs with thermal pads utilize via structures that are either open or filled. In the case of open via structure designs, solder intended for the thermal pad can travel down thermal vias robbing the pad structure of desired solder volume leading to inconsistent component standoff/reliability, I/O opens, increased rework difficulties, and underside solder shards – with longer-term system level shorting risks. Alternatively, filled thermal via design points, ensure a planar surface is created upon which to solder the component to the thermal pad. Solder mask ‘via tenting’, encroached vias, and costly via in pad plated over (VIPPO) techniques are widely used across the industry to achieve this. While many of these options may be suitable for some electronic hardware products – manufacturability trade-offs, reliability, and cost impacts may limit usage in some high complexity, high reliability applications. This paper introduces a new alternative using QFNs with open thermal via-in-pad (VIP) structures. The design point discussed utilizes conventional PCB through-hole via technology that is not plugged nor filled in any manner, ensures proper via sizes/pitch/counts/locations are achieved, and incorporates custom solder mask window patterns overtop copper thermal pad areas. The solution enables a lower cost PCB compared to VIPPO structures, eliminates the possibility of solder wicking down via structures, and significantly improves component assembly/reworkablity. In addition, it helps maximize thermal, power, and interconnect reliability of QFN packages. Results from fourteen months of development and optimization are included. The importance of designing for thermal, power, and signal integrity considerations are discussed. Manufacturing quality and reworkability are also of key interest. The intent of the paper is to offer a new design solution as an option to published methods.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".