Selective Wave Soldering DOE to Develop DFM Guidelines for Lead and Lead-Free Assemblies
Bibliographic record
Abstract
ABSTRACT The desire to constantly push the limits of signal integrity and reduce material costs by minimizing component spacing is a continual requirement for printed circuit board designers. Unfortunately, in some cases these design objectives can conflict with the manufacturability of a product. For instance, the tight spacing of bottomside surface mount devices (SMT) placed next to pin-through-hole (PTH) connectors can make the process of soldering the PTH connectors in accordance with IPC-A-610 barrel fill specifications very difficult. In these cases, a selective wave soldering process is required. This is a process of using product specific wave solder pallets which are designed to shield the surface mount components placed on the bottomside of a printed circuit board while exposed through-hole connector locations are wave soldered. The reduction in the pallet opening size on a selective wave solder pallet reduces the ability to successfully fill PTH barrels. This is the case when using tin lead (SnPb) alloy, however, the problem is further amplified when converting to a lead free (Pb-free) alloy due to the differences in fluid properties which exist between these alloy types. Currently, there are no industry standards for minimum pad-to-pad spacing for bottomside SMT to PTH components for Pb-free. Most EMS and OEM companies have established acceptable Design for Manufacturability (DFM) guidelines when using SnPb alloy, based on many years of experience. However, it has been found that DFM guidelines which were established for SnPb processes in many cases do not result in the same level of quality joints when soldering with Pb-free alloy. Therefore, in order to maintain the process yields and minimize manufacturing costs when converting to Pb-free, it is essential to establish DFM guidelines specifically for Pb-free soldering. This paper will discuss the outcome of a study of several DFM features incorporated on a custom designed test vehicle. Specifically, a Design of Experiment (DoE) was established to test the limits of pad-to-pad (P2P) component spacing, in order to confirm the acceptable limits when using SnPb (63Sn-37Pb) alloy and to compare and define limits when using Pb-free (Sn-3.0Ag-0.5Cu) alloy. In addition to this, other DFM aspects were also studied such as the effect of pin-to-hole ratio and its interaction with the quantity of large copper planes connected to a PTH barrel and the effect of the type of connection – either solid or four spoke thermal relief. In addition, the ability of a standard wave pallet to shield bottomside SMT components from excessive heat during wave soldering is measured. The test vehicle was assembled using 5 different selective wave pallets, each with varying opening sizes to accommodate various levels of pad-to-pad spacing. The quality level of each of the described DFM features will be discussed, primarily focusing on the ability to achieve acceptable levels of barrel fill according to IPC-A-610 specifications [1].
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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 | 0.015 | 0.020 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.005 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.003 | 0.002 |
| Research integrity | 0.003 | 0.002 |
| Insufficient payload (model declined to judge) | 0.005 | 0.006 |
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".