Expunged records should not show on background checks in Pennsylvania. When a record is expunged in Pennsylvania, the record should be destroyed per Pennsylvania law. When an expungement order is granted, it gets served upon all applicable law enforcement, government and court agencies. For example, the magisterial district court, the arresting police department, the District Attorney's Office, the Court of Common Pleas, in a sense self-serves itself, the Administrative Office of Pennsylvania Courts, the AOPC.
There could be other agencies involved, probation, the jail, the sheriff's department, the Pennsylvania State Police, the Pennsylvania State Police in turn forward, and expansion boards to the FBI per standard practice. The Pennsylvania State Police, they're the most important repository of criminal records in Pennsylvania. When employers are seeking or doing a background check on a person, whether internally or if they use an outside organization or third party, they generally would go to the Pennsylvania State Police for those records. With an expungement, the Pennsylvania State Police would no longer have those records on the record, so an expunged record should not be on a background check.
Certain people have certain additional considerations, licensed professionals and so forth, so in terms of how they may have to respond to questions regarding a criminal record. Having an experienced Pennsylvania criminal defense attorney will help you best understand the expungement process and best navigate the process. They should be involved as early as possible in your case.